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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-06 01:02:30 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-06 01:02:30 +0000 |
| commit | 76cb841cb886eef6b3bee341a2266c76578724ad (patch) | |
| tree | f5892e5ba6cc11949952a6ce4ecbe6d516d6ce58 /Documentation/trace | |
| parent | Initial commit. (diff) | |
| download | linux-c109f8d9e922037b3fa45f46d78384d49db8ad76.tar.xz linux-c109f8d9e922037b3fa45f46d78384d49db8ad76.zip | |
Adding upstream version 4.19.249.upstream/4.19.249upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/trace')
25 files changed, 11674 insertions, 0 deletions
diff --git a/Documentation/trace/coresight-cpu-debug.txt b/Documentation/trace/coresight-cpu-debug.txt new file mode 100644 index 000000000..89ab09e78 --- /dev/null +++ b/Documentation/trace/coresight-cpu-debug.txt @@ -0,0 +1,187 @@ + Coresight CPU Debug Module + ========================== + + Author: Leo Yan <leo.yan@linaro.org> + Date: April 5th, 2017 + +Introduction +------------ + +Coresight CPU debug module is defined in ARMv8-a architecture reference manual +(ARM DDI 0487A.k) Chapter 'Part H: External debug', the CPU can integrate +debug module and it is mainly used for two modes: self-hosted debug and +external debug. Usually the external debug mode is well known as the external +debugger connects with SoC from JTAG port; on the other hand the program can +explore debugging method which rely on self-hosted debug mode, this document +is to focus on this part. + +The debug module provides sample-based profiling extension, which can be used +to sample CPU program counter, secure state and exception level, etc; usually +every CPU has one dedicated debug module to be connected. Based on self-hosted +debug mechanism, Linux kernel can access these related registers from mmio +region when the kernel panic happens. The callback notifier for kernel panic +will dump related registers for every CPU; finally this is good for assistant +analysis for panic. + + +Implementation +-------------- + +- During driver registration, it uses EDDEVID and EDDEVID1 - two device ID + registers to decide if sample-based profiling is implemented or not. On some + platforms this hardware feature is fully or partially implemented; and if + this feature is not supported then registration will fail. + +- At the time this documentation was written, the debug driver mainly relies on + information gathered by the kernel panic callback notifier from three + sampling registers: EDPCSR, EDVIDSR and EDCIDSR: from EDPCSR we can get + program counter; EDVIDSR has information for secure state, exception level, + bit width, etc; EDCIDSR is context ID value which contains the sampled value + of CONTEXTIDR_EL1. + +- The driver supports a CPU running in either AArch64 or AArch32 mode. The + registers naming convention is a bit different between them, AArch64 uses + 'ED' for register prefix (ARM DDI 0487A.k, chapter H9.1) and AArch32 uses + 'DBG' as prefix (ARM DDI 0487A.k, chapter G5.1). The driver is unified to + use AArch64 naming convention. + +- ARMv8-a (ARM DDI 0487A.k) and ARMv7-a (ARM DDI 0406C.b) have different + register bits definition. So the driver consolidates two difference: + + If PCSROffset=0b0000, on ARMv8-a the feature of EDPCSR is not implemented; + but ARMv7-a defines "PCSR samples are offset by a value that depends on the + instruction set state". For ARMv7-a, the driver checks furthermore if CPU + runs with ARM or thumb instruction set and calibrate PCSR value, the + detailed description for offset is in ARMv7-a ARM (ARM DDI 0406C.b) chapter + C11.11.34 "DBGPCSR, Program Counter Sampling Register". + + If PCSROffset=0b0010, ARMv8-a defines "EDPCSR implemented, and samples have + no offset applied and do not sample the instruction set state in AArch32 + state". So on ARMv8 if EDDEVID1.PCSROffset is 0b0010 and the CPU operates + in AArch32 state, EDPCSR is not sampled; when the CPU operates in AArch64 + state EDPCSR is sampled and no offset are applied. + + +Clock and power domain +---------------------- + +Before accessing debug registers, we should ensure the clock and power domain +have been enabled properly. In ARMv8-a ARM (ARM DDI 0487A.k) chapter 'H9.1 +Debug registers', the debug registers are spread into two domains: the debug +domain and the CPU domain. + + +---------------+ + | | + | | + +----------+--+ | + dbg_clock -->| |**| |<-- cpu_clock + | Debug |**| CPU | + dbg_power_domain -->| |**| |<-- cpu_power_domain + +----------+--+ | + | | + | | + +---------------+ + +For debug domain, the user uses DT binding "clocks" and "power-domains" to +specify the corresponding clock source and power supply for the debug logic. +The driver calls the pm_runtime_{put|get} operations as needed to handle the +debug power domain. + +For CPU domain, the different SoC designs have different power management +schemes and finally this heavily impacts external debug module. So we can +divide into below cases: + +- On systems with a sane power controller which can behave correctly with + respect to CPU power domain, the CPU power domain can be controlled by + register EDPRCR in driver. The driver firstly writes bit EDPRCR.COREPURQ + to power up the CPU, and then writes bit EDPRCR.CORENPDRQ for emulation + of CPU power down. As result, this can ensure the CPU power domain is + powered on properly during the period when access debug related registers; + +- Some designs will power down an entire cluster if all CPUs on the cluster + are powered down - including the parts of the debug registers that should + remain powered in the debug power domain. The bits in EDPRCR are not + respected in these cases, so these designs do not support debug over + power down in the way that the CoreSight / Debug designers anticipated. + This means that even checking EDPRSR has the potential to cause a bus hang + if the target register is unpowered. + + In this case, accessing to the debug registers while they are not powered + is a recipe for disaster; so we need preventing CPU low power states at boot + time or when user enable module at the run time. Please see chapter + "How to use the module" for detailed usage info for this. + + +Device Tree Bindings +-------------------- + +See Documentation/devicetree/bindings/arm/coresight-cpu-debug.txt for details. + + +How to use the module +--------------------- + +If you want to enable debugging functionality at boot time, you can add +"coresight_cpu_debug.enable=1" to the kernel command line parameter. + +The driver also can work as module, so can enable the debugging when insmod +module: +# insmod coresight_cpu_debug.ko debug=1 + +When boot time or insmod module you have not enabled the debugging, the driver +uses the debugfs file system to provide a knob to dynamically enable or disable +debugging: + +To enable it, write a '1' into /sys/kernel/debug/coresight_cpu_debug/enable: +# echo 1 > /sys/kernel/debug/coresight_cpu_debug/enable + +To disable it, write a '0' into /sys/kernel/debug/coresight_cpu_debug/enable: +# echo 0 > /sys/kernel/debug/coresight_cpu_debug/enable + +As explained in chapter "Clock and power domain", if you are working on one +platform which has idle states to power off debug logic and the power +controller cannot work well for the request from EDPRCR, then you should +firstly constraint CPU idle states before enable CPU debugging feature; so can +ensure the accessing to debug logic. + +If you want to limit idle states at boot time, you can use "nohlt" or +"cpuidle.off=1" in the kernel command line. + +At the runtime you can disable idle states with below methods: + +It is possible to disable CPU idle states by way of the PM QoS +subsystem, more specifically by using the "/dev/cpu_dma_latency" +interface (see Documentation/power/pm_qos_interface.txt for more +details). As specified in the PM QoS documentation the requested +parameter will stay in effect until the file descriptor is released. +For example: + +# exec 3<> /dev/cpu_dma_latency; echo 0 >&3 +... +Do some work... +... +# exec 3<>- + +The same can also be done from an application program. + +Disable specific CPU's specific idle state from cpuidle sysfs (see +Documentation/cpuidle/sysfs.txt): +# echo 1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable + + +Output format +------------- + +Here is an example of the debugging output format: + +ARM external debug module: +coresight-cpu-debug 850000.debug: CPU[0]: +coresight-cpu-debug 850000.debug: EDPRSR: 00000001 (Power:On DLK:Unlock) +coresight-cpu-debug 850000.debug: EDPCSR: handle_IPI+0x174/0x1d8 +coresight-cpu-debug 850000.debug: EDCIDSR: 00000000 +coresight-cpu-debug 850000.debug: EDVIDSR: 90000000 (State:Non-secure Mode:EL1/0 Width:64bits VMID:0) +coresight-cpu-debug 852000.debug: CPU[1]: +coresight-cpu-debug 852000.debug: EDPRSR: 00000001 (Power:On DLK:Unlock) +coresight-cpu-debug 852000.debug: EDPCSR: debug_notifier_call+0x23c/0x358 +coresight-cpu-debug 852000.debug: EDCIDSR: 00000000 +coresight-cpu-debug 852000.debug: EDVIDSR: 90000000 (State:Non-secure Mode:EL1/0 Width:64bits VMID:0) diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt new file mode 100644 index 000000000..efbc83214 --- /dev/null +++ b/Documentation/trace/coresight.txt @@ -0,0 +1,430 @@ + Coresight - HW Assisted Tracing on ARM + ====================================== + + Author: Mathieu Poirier <mathieu.poirier@linaro.org> + Date: September 11th, 2014 + +Introduction +------------ + +Coresight is an umbrella of technologies allowing for the debugging of ARM +based SoC. It includes solutions for JTAG and HW assisted tracing. This +document is concerned with the latter. + +HW assisted tracing is becoming increasingly useful when dealing with systems +that have many SoCs and other components like GPU and DMA engines. ARM has +developed a HW assisted tracing solution by means of different components, each +being added to a design at synthesis time to cater to specific tracing needs. +Components are generally categorised as source, link and sinks and are +(usually) discovered using the AMBA bus. + +"Sources" generate a compressed stream representing the processor instruction +path based on tracing scenarios as configured by users. From there the stream +flows through the coresight system (via ATB bus) using links that are connecting +the emanating source to a sink(s). Sinks serve as endpoints to the coresight +implementation, either storing the compressed stream in a memory buffer or +creating an interface to the outside world where data can be transferred to a +host without fear of filling up the onboard coresight memory buffer. + +At typical coresight system would look like this: + + ***************************************************************** + **************************** AMBA AXI ****************************===|| + ***************************************************************** || + ^ ^ | || + | | * ** + 0000000 ::::: 0000000 ::::: ::::: @@@@@@@ |||||||||||| + 0 CPU 0<-->: C : 0 CPU 0<-->: C : : C : @ STM @ || System || + |->0000000 : T : |->0000000 : T : : T :<--->@@@@@ || Memory || + | #######<-->: I : | #######<-->: I : : I : @@@<-| |||||||||||| + | # ETM # ::::: | # PTM # ::::: ::::: @ | + | ##### ^ ^ | ##### ^ ! ^ ! . | ||||||||| + | |->### | ! | |->### | ! | ! . | || DAP || + | | # | ! | | # | ! | ! . | ||||||||| + | | . | ! | | . | ! | ! . | | | + | | . | ! | | . | ! | ! . | | * + | | . | ! | | . | ! | ! . | | SWD/ + | | . | ! | | . | ! | ! . | | JTAG + *****************************************************************<-| + *************************** AMBA Debug APB ************************ + ***************************************************************** + | . ! . ! ! . | + | . * . * * . | + ***************************************************************** + ******************** Cross Trigger Matrix (CTM) ******************* + ***************************************************************** + | . ^ . . | + | * ! * * | + ***************************************************************** + ****************** AMBA Advanced Trace Bus (ATB) ****************** + ***************************************************************** + | ! =============== | + | * ===== F =====<---------| + | ::::::::: ==== U ==== + |-->:: CTI ::<!! === N === + | ::::::::: ! == N == + | ^ * == E == + | ! &&&&&&&&& IIIIIII == L == + |------>&& ETB &&<......II I ======= + | ! &&&&&&&&& II I . + | ! I I . + | ! I REP I<.......... + | ! I I + | !!>&&&&&&&&& II I *Source: ARM ltd. + |------>& TPIU &<......II I DAP = Debug Access Port + &&&&&&&&& IIIIIII ETM = Embedded Trace Macrocell + ; PTM = Program Trace Macrocell + ; CTI = Cross Trigger Interface + * ETB = Embedded Trace Buffer + To trace port TPIU= Trace Port Interface Unit + SWD = Serial Wire Debug + +While on target configuration of the components is done via the APB bus, +all trace data are carried out-of-band on the ATB bus. The CTM provides +a way to aggregate and distribute signals between CoreSight components. + +The coresight framework provides a central point to represent, configure and +manage coresight devices on a platform. This first implementation centers on +the basic tracing functionality, enabling components such ETM/PTM, funnel, +replicator, TMC, TPIU and ETB. Future work will enable more +intricate IP blocks such as STM and CTI. + + +Acronyms and Classification +--------------------------- + +Acronyms: + +PTM: Program Trace Macrocell +ETM: Embedded Trace Macrocell +STM: System trace Macrocell +ETB: Embedded Trace Buffer +ITM: Instrumentation Trace Macrocell +TPIU: Trace Port Interface Unit +TMC-ETR: Trace Memory Controller, configured as Embedded Trace Router +TMC-ETF: Trace Memory Controller, configured as Embedded Trace FIFO +CTI: Cross Trigger Interface + +Classification: + +Source: + ETMv3.x ETMv4, PTMv1.0, PTMv1.1, STM, STM500, ITM +Link: + Funnel, replicator (intelligent or not), TMC-ETR +Sinks: + ETBv1.0, ETB1.1, TPIU, TMC-ETF +Misc: + CTI + + +Device Tree Bindings +---------------------- + +See Documentation/devicetree/bindings/arm/coresight.txt for details. + +As of this writing drivers for ITM, STMs and CTIs are not provided but are +expected to be added as the solution matures. + + +Framework and implementation +---------------------------- + +The coresight framework provides a central point to represent, configure and +manage coresight devices on a platform. Any coresight compliant device can +register with the framework for as long as they use the right APIs: + +struct coresight_device *coresight_register(struct coresight_desc *desc); +void coresight_unregister(struct coresight_device *csdev); + +The registering function is taking a "struct coresight_device *csdev" and +register the device with the core framework. The unregister function takes +a reference to a "struct coresight_device", obtained at registration time. + +If everything goes well during the registration process the new devices will +show up under /sys/bus/coresight/devices, as showns here for a TC2 platform: + +root:~# ls /sys/bus/coresight/devices/ +replicator 20030000.tpiu 2201c000.ptm 2203c000.etm 2203e000.etm +20010000.etb 20040000.funnel 2201d000.ptm 2203d000.etm +root:~# + +The functions take a "struct coresight_device", which looks like this: + +struct coresight_desc { + enum coresight_dev_type type; + struct coresight_dev_subtype subtype; + const struct coresight_ops *ops; + struct coresight_platform_data *pdata; + struct device *dev; + const struct attribute_group **groups; +}; + + +The "coresight_dev_type" identifies what the device is, i.e, source link or +sink while the "coresight_dev_subtype" will characterise that type further. + +The "struct coresight_ops" is mandatory and will tell the framework how to +perform base operations related to the components, each component having +a different set of requirement. For that "struct coresight_ops_sink", +"struct coresight_ops_link" and "struct coresight_ops_source" have been +provided. + +The next field, "struct coresight_platform_data *pdata" is acquired by calling +"of_get_coresight_platform_data()", as part of the driver's _probe routine and +"struct device *dev" gets the device reference embedded in the "amba_device": + +static int etm_probe(struct amba_device *adev, const struct amba_id *id) +{ + ... + ... + drvdata->dev = &adev->dev; + ... +} + +Specific class of device (source, link, or sink) have generic operations +that can be performed on them (see "struct coresight_ops"). The +"**groups" is a list of sysfs entries pertaining to operations +specific to that component only. "Implementation defined" customisations are +expected to be accessed and controlled using those entries. + + +How to use the tracer modules +----------------------------- + +There are two ways to use the Coresight framework: 1) using the perf cmd line +tools and 2) interacting directly with the Coresight devices using the sysFS +interface. Preference is given to the former as using the sysFS interface +requires a deep understanding of the Coresight HW. The following sections +provide details on using both methods. + +1) Using the sysFS interface: + +Before trace collection can start, a coresight sink needs to be identified. +There is no limit on the amount of sinks (nor sources) that can be enabled at +any given moment. As a generic operation, all device pertaining to the sink +class will have an "active" entry in sysfs: + +root:/sys/bus/coresight/devices# ls +replicator 20030000.tpiu 2201c000.ptm 2203c000.etm 2203e000.etm +20010000.etb 20040000.funnel 2201d000.ptm 2203d000.etm +root:/sys/bus/coresight/devices# ls 20010000.etb +enable_sink status trigger_cntr +root:/sys/bus/coresight/devices# echo 1 > 20010000.etb/enable_sink +root:/sys/bus/coresight/devices# cat 20010000.etb/enable_sink +1 +root:/sys/bus/coresight/devices# + +At boot time the current etm3x driver will configure the first address +comparator with "_stext" and "_etext", essentially tracing any instruction +that falls within that range. As such "enabling" a source will immediately +trigger a trace capture: + +root:/sys/bus/coresight/devices# echo 1 > 2201c000.ptm/enable_source +root:/sys/bus/coresight/devices# cat 2201c000.ptm/enable_source +1 +root:/sys/bus/coresight/devices# cat 20010000.etb/status +Depth: 0x2000 +Status: 0x1 +RAM read ptr: 0x0 +RAM wrt ptr: 0x19d3 <----- The write pointer is moving +Trigger cnt: 0x0 +Control: 0x1 +Flush status: 0x0 +Flush ctrl: 0x2001 +root:/sys/bus/coresight/devices# + +Trace collection is stopped the same way: + +root:/sys/bus/coresight/devices# echo 0 > 2201c000.ptm/enable_source +root:/sys/bus/coresight/devices# + +The content of the ETB buffer can be harvested directly from /dev: + +root:/sys/bus/coresight/devices# dd if=/dev/20010000.etb \ +of=~/cstrace.bin + +64+0 records in +64+0 records out +32768 bytes (33 kB) copied, 0.00125258 s, 26.2 MB/s +root:/sys/bus/coresight/devices# + +The file cstrace.bin can be decompressed using "ptm2human", DS-5 or Trace32. + +Following is a DS-5 output of an experimental loop that increments a variable up +to a certain value. The example is simple and yet provides a glimpse of the +wealth of possibilities that coresight provides. + +Info Tracing enabled +Instruction 106378866 0x8026B53C E52DE004 false PUSH {lr} +Instruction 0 0x8026B540 E24DD00C false SUB sp,sp,#0xc +Instruction 0 0x8026B544 E3A03000 false MOV r3,#0 +Instruction 0 0x8026B548 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Timestamp Timestamp: 17106715833 +Instruction 319 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 9 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 7 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 7 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 10 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 6 0x8026B560 EE1D3F30 false MRC p15,#0x0,r3,c13,c0,#1 +Instruction 0 0x8026B564 E1A0100D false MOV r1,sp +Instruction 0 0x8026B568 E3C12D7F false BIC r2,r1,#0x1fc0 +Instruction 0 0x8026B56C E3C2203F false BIC r2,r2,#0x3f +Instruction 0 0x8026B570 E59D1004 false LDR r1,[sp,#4] +Instruction 0 0x8026B574 E59F0010 false LDR r0,[pc,#16] ; [0x8026B58C] = 0x80550368 +Instruction 0 0x8026B578 E592200C false LDR r2,[r2,#0xc] +Instruction 0 0x8026B57C E59221D0 false LDR r2,[r2,#0x1d0] +Instruction 0 0x8026B580 EB07A4CF true BL {pc}+0x1e9344 ; 0x804548c4 +Info Tracing enabled +Instruction 13570831 0x8026B584 E28DD00C false ADD sp,sp,#0xc +Instruction 0 0x8026B588 E8BD8000 true LDM sp!,{pc} +Timestamp Timestamp: 17107041535 + +2) Using perf framework: + +Coresight tracers are represented using the Perf framework's Performance +Monitoring Unit (PMU) abstraction. As such the perf framework takes charge of +controlling when tracing gets enabled based on when the process of interest is +scheduled. When configured in a system, Coresight PMUs will be listed when +queried by the perf command line tool: + + linaro@linaro-nano:~$ ./perf list pmu + + List of pre-defined events (to be used in -e): + + cs_etm// [Kernel PMU event] + + linaro@linaro-nano:~$ + +Regardless of the number of tracers available in a system (usually equal to the +amount of processor cores), the "cs_etm" PMU will be listed only once. + +A Coresight PMU works the same way as any other PMU, i.e the name of the PMU is +listed along with configuration options within forward slashes '/'. Since a +Coresight system will typically have more than one sink, the name of the sink to +work with needs to be specified as an event option. Names for sink to choose +from are listed in sysFS under ($SYSFS)/bus/coresight/devices: + + root@linaro-nano:~# ls /sys/bus/coresight/devices/ + 20010000.etf 20040000.funnel 20100000.stm 22040000.etm + 22140000.etm 230c0000.funnel 23240000.etm 20030000.tpiu + 20070000.etr 20120000.replicator 220c0000.funnel + 23040000.etm 23140000.etm 23340000.etm + + root@linaro-nano:~# perf record -e cs_etm/@20070000.etr/u --per-thread program + +The syntax within the forward slashes '/' is important. The '@' character +tells the parser that a sink is about to be specified and that this is the sink +to use for the trace session. + +More information on the above and other example on how to use Coresight with +the perf tools can be found in the "HOWTO.md" file of the openCSD gitHub +repository [3]. + +2.1) AutoFDO analysis using the perf tools: + +perf can be used to record and analyze trace of programs. + +Execution can be recorded using 'perf record' with the cs_etm event, +specifying the name of the sink to record to, e.g: + + perf record -e cs_etm/@20070000.etr/u --per-thread + +The 'perf report' and 'perf script' commands can be used to analyze execution, +synthesizing instruction and branch events from the instruction trace. +'perf inject' can be used to replace the trace data with the synthesized events. +The --itrace option controls the type and frequency of synthesized events +(see perf documentation). + +Note that only 64-bit programs are currently supported - further work is +required to support instruction decode of 32-bit Arm programs. + + +Generating coverage files for Feedback Directed Optimization: AutoFDO +--------------------------------------------------------------------- + +'perf inject' accepts the --itrace option in which case tracing data is +removed and replaced with the synthesized events. e.g. + + perf inject --itrace --strip -i perf.data -o perf.data.new + +Below is an example of using ARM ETM for autoFDO. It requires autofdo +(https://github.com/google/autofdo) and gcc version 5. The bubble +sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial). + + $ gcc-5 -O3 sort.c -o sort + $ taskset -c 2 ./sort + Bubble sorting array of 30000 elements + 5910 ms + + $ perf record -e cs_etm/@20070000.etr/u --per-thread taskset -c 2 ./sort + Bubble sorting array of 30000 elements + 12543 ms + [ perf record: Woken up 35 times to write data ] + [ perf record: Captured and wrote 69.640 MB perf.data ] + + $ perf inject -i perf.data -o inj.data --itrace=il64 --strip + $ create_gcov --binary=./sort --profile=inj.data --gcov=sort.gcov -gcov_version=1 + $ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo + $ taskset -c 2 ./sort_autofdo + Bubble sorting array of 30000 elements + 5806 ms + + +How to use the STM module +------------------------- + +Using the System Trace Macrocell module is the same as the tracers - the only +difference is that clients are driving the trace capture rather +than the program flow through the code. + +As with any other CoreSight component, specifics about the STM tracer can be +found in sysfs with more information on each entry being found in [1]: + +root@genericarmv8:~# ls /sys/bus/coresight/devices/20100000.stm +enable_source hwevent_select port_enable subsystem uevent +hwevent_enable mgmt port_select traceid +root@genericarmv8:~# + +Like any other source a sink needs to be identified and the STM enabled before +being used: + +root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20010000.etf/enable_sink +root@genericarmv8:~# echo 1 > /sys/bus/coresight/devices/20100000.stm/enable_source + +From there user space applications can request and use channels using the devfs +interface provided for that purpose by the generic STM API: + +root@genericarmv8:~# ls -l /dev/20100000.stm +crw------- 1 root root 10, 61 Jan 3 18:11 /dev/20100000.stm +root@genericarmv8:~# + +Details on how to use the generic STM API can be found here [2]. + +[1]. Documentation/ABI/testing/sysfs-bus-coresight-devices-stm +[2]. Documentation/trace/stm.rst +[3]. https://github.com/Linaro/perf-opencsd diff --git a/Documentation/trace/events-kmem.rst b/Documentation/trace/events-kmem.rst new file mode 100644 index 000000000..555484110 --- /dev/null +++ b/Documentation/trace/events-kmem.rst @@ -0,0 +1,119 @@ +============================ +Subsystem Trace Points: kmem +============================ + +The kmem tracing system captures events related to object and page allocation +within the kernel. Broadly speaking there are five major subheadings. + + - Slab allocation of small objects of unknown type (kmalloc) + - Slab allocation of small objects of known type + - Page allocation + - Per-CPU Allocator Activity + - External Fragmentation + +This document describes what each of the tracepoints is and why they +might be useful. + +1. Slab allocation of small objects of unknown type +=================================================== +:: + + kmalloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s + kmalloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d + kfree call_site=%lx ptr=%p + +Heavy activity for these events may indicate that a specific cache is +justified, particularly if kmalloc slab pages are getting significantly +internal fragmented as a result of the allocation pattern. By correlating +kmalloc with kfree, it may be possible to identify memory leaks and where +the allocation sites were. + + +2. Slab allocation of small objects of known type +================================================= +:: + + kmem_cache_alloc call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s + kmem_cache_alloc_node call_site=%lx ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s node=%d + kmem_cache_free call_site=%lx ptr=%p + +These events are similar in usage to the kmalloc-related events except that +it is likely easier to pin the event down to a specific cache. At the time +of writing, no information is available on what slab is being allocated from, +but the call_site can usually be used to extrapolate that information. + +3. Page allocation +================== +:: + + mm_page_alloc page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s + mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d + mm_page_free page=%p pfn=%lu order=%d + mm_page_free_batched page=%p pfn=%lu order=%d cold=%d + +These four events deal with page allocation and freeing. mm_page_alloc is +a simple indicator of page allocator activity. Pages may be allocated from +the per-CPU allocator (high performance) or the buddy allocator. + +If pages are allocated directly from the buddy allocator, the +mm_page_alloc_zone_locked event is triggered. This event is important as high +amounts of activity imply high activity on the zone->lock. Taking this lock +impairs performance by disabling interrupts, dirtying cache lines between +CPUs and serialising many CPUs. + +When a page is freed directly by the caller, the only mm_page_free event +is triggered. Significant amounts of activity here could indicate that the +callers should be batching their activities. + +When pages are freed in batch, the also mm_page_free_batched is triggered. +Broadly speaking, pages are taken off the LRU lock in bulk and +freed in batch with a page list. Significant amounts of activity here could +indicate that the system is under memory pressure and can also indicate +contention on the zone->lru_lock. + +4. Per-CPU Allocator Activity +============================= +:: + + mm_page_alloc_zone_locked page=%p pfn=%lu order=%u migratetype=%d cpu=%d percpu_refill=%d + mm_page_pcpu_drain page=%p pfn=%lu order=%d cpu=%d migratetype=%d + +In front of the page allocator is a per-cpu page allocator. It exists only +for order-0 pages, reduces contention on the zone->lock and reduces the +amount of writing on struct page. + +When a per-CPU list is empty or pages of the wrong type are allocated, +the zone->lock will be taken once and the per-CPU list refilled. The event +triggered is mm_page_alloc_zone_locked for each page allocated with the +event indicating whether it is for a percpu_refill or not. + +When the per-CPU list is too full, a number of pages are freed, each one +which triggers a mm_page_pcpu_drain event. + +The individual nature of the events is so that pages can be tracked +between allocation and freeing. A number of drain or refill pages that occur +consecutively imply the zone->lock being taken once. Large amounts of per-CPU +refills and drains could imply an imbalance between CPUs where too much work +is being concentrated in one place. It could also indicate that the per-CPU +lists should be a larger size. Finally, large amounts of refills on one CPU +and drains on another could be a factor in causing large amounts of cache +line bounces due to writes between CPUs and worth investigating if pages +can be allocated and freed on the same CPU through some algorithm change. + +5. External Fragmentation +========================= +:: + + mm_page_alloc_extfrag page=%p pfn=%lu alloc_order=%d fallback_order=%d pageblock_order=%d alloc_migratetype=%d fallback_migratetype=%d fragmenting=%d change_ownership=%d + +External fragmentation affects whether a high-order allocation will be +successful or not. For some types of hardware, this is important although +it is avoided where possible. If the system is using huge pages and needs +to be able to resize the pool over the lifetime of the system, this value +is important. + +Large numbers of this event implies that memory is fragmenting and +high-order allocations will start failing at some time in the future. One +means of reducing the occurrence of this event is to increase the size of +min_free_kbytes in increments of 3*pageblock_size*nr_online_nodes where +pageblock_size is usually the size of the default hugepage size. diff --git a/Documentation/trace/events-msr.rst b/Documentation/trace/events-msr.rst new file mode 100644 index 000000000..e938aa0b6 --- /dev/null +++ b/Documentation/trace/events-msr.rst @@ -0,0 +1,40 @@ +================ +MSR Trace Events +================ + +The x86 kernel supports tracing most MSR (Model Specific Register) accesses. +To see the definition of the MSRs on Intel systems please see the SDM +at http://www.intel.com/sdm (Volume 3) + +Available trace points: + +/sys/kernel/debug/tracing/events/msr/ + +Trace MSR reads: + +read_msr + + - msr: MSR number + - val: Value written + - failed: 1 if the access failed, otherwise 0 + + +Trace MSR writes: + +write_msr + + - msr: MSR number + - val: Value written + - failed: 1 if the access failed, otherwise 0 + + +Trace RDPMC in kernel: + +rdpmc + +The trace data can be post processed with the postprocess/decode_msr.py script:: + + cat /sys/kernel/debug/tracing/trace | decode_msr.py /usr/src/linux/include/asm/msr-index.h + +to add symbolic MSR names. + diff --git a/Documentation/trace/events-nmi.rst b/Documentation/trace/events-nmi.rst new file mode 100644 index 000000000..9e0a7289d --- /dev/null +++ b/Documentation/trace/events-nmi.rst @@ -0,0 +1,45 @@ +================ +NMI Trace Events +================ + +These events normally show up here: + + /sys/kernel/debug/tracing/events/nmi + + +nmi_handler +----------- + +You might want to use this tracepoint if you suspect that your +NMI handlers are hogging large amounts of CPU time. The kernel +will warn if it sees long-running handlers:: + + INFO: NMI handler took too long to run: 9.207 msecs + +and this tracepoint will allow you to drill down and get some +more details. + +Let's say you suspect that perf_event_nmi_handler() is causing +you some problems and you only want to trace that handler +specifically. You need to find its address:: + + $ grep perf_event_nmi_handler /proc/kallsyms + ffffffff81625600 t perf_event_nmi_handler + +Let's also say you are only interested in when that function is +really hogging a lot of CPU time, like a millisecond at a time. +Note that the kernel's output is in milliseconds, but the input +to the filter is in nanoseconds! You can filter on 'delta_ns':: + + cd /sys/kernel/debug/tracing/events/nmi/nmi_handler + echo 'handler==0xffffffff81625600 && delta_ns>1000000' > filter + echo 1 > enable + +Your output would then look like:: + + $ cat /sys/kernel/debug/tracing/trace_pipe + <idle>-0 [000] d.h3 505.397558: nmi_handler: perf_event_nmi_handler() delta_ns: 3236765 handled: 1 + <idle>-0 [000] d.h3 505.805893: nmi_handler: perf_event_nmi_handler() delta_ns: 3174234 handled: 1 + <idle>-0 [000] d.h3 506.158206: nmi_handler: perf_event_nmi_handler() delta_ns: 3084642 handled: 1 + <idle>-0 [000] d.h3 506.334346: nmi_handler: perf_event_nmi_handler() delta_ns: 3080351 handled: 1 + diff --git a/Documentation/trace/events-power.rst b/Documentation/trace/events-power.rst new file mode 100644 index 000000000..2ef318962 --- /dev/null +++ b/Documentation/trace/events-power.rst @@ -0,0 +1,105 @@ +============================= +Subsystem Trace Points: power +============================= + +The power tracing system captures events related to power transitions +within the kernel. Broadly speaking there are three major subheadings: + + - Power state switch which reports events related to suspend (S-states), + cpuidle (C-states) and cpufreq (P-states) + - System clock related changes + - Power domains related changes and transitions + +This document describes what each of the tracepoints is and why they +might be useful. + +Cf. include/trace/events/power.h for the events definitions. + +1. Power state switch events +============================ + +1.1 Trace API +----------------- + +A 'cpu' event class gathers the CPU-related events: cpuidle and +cpufreq. +:: + + cpu_idle "state=%lu cpu_id=%lu" + cpu_frequency "state=%lu cpu_id=%lu" + cpu_frequency_limits "min=%lu max=%lu cpu_id=%lu" + +A suspend event is used to indicate the system going in and out of the +suspend mode: +:: + + machine_suspend "state=%lu" + + +Note: the value of '-1' or '4294967295' for state means an exit from the current state, +i.e. trace_cpu_idle(4, smp_processor_id()) means that the system +enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()) +means that the system exits the previous idle state. + +The event which has 'state=4294967295' in the trace is very important to the user +space tools which are using it to detect the end of the current state, and so to +correctly draw the states diagrams and to calculate accurate statistics etc. + +2. Clocks events +================ +The clock events are used for clock enable/disable and for +clock rate change. +:: + + clock_enable "%s state=%lu cpu_id=%lu" + clock_disable "%s state=%lu cpu_id=%lu" + clock_set_rate "%s state=%lu cpu_id=%lu" + +The first parameter gives the clock name (e.g. "gpio1_iclk"). +The second parameter is '1' for enable, '0' for disable, the target +clock rate for set_rate. + +3. Power domains events +======================= +The power domain events are used for power domains transitions +:: + + power_domain_target "%s state=%lu cpu_id=%lu" + +The first parameter gives the power domain name (e.g. "mpu_pwrdm"). +The second parameter is the power domain target state. + +4. PM QoS events +================ +The PM QoS events are used for QoS add/update/remove request and for +target/flags update. +:: + + pm_qos_add_request "pm_qos_class=%s value=%d" + pm_qos_update_request "pm_qos_class=%s value=%d" + pm_qos_remove_request "pm_qos_class=%s value=%d" + pm_qos_update_request_timeout "pm_qos_class=%s value=%d, timeout_us=%ld" + +The first parameter gives the QoS class name (e.g. "CPU_DMA_LATENCY"). +The second parameter is value to be added/updated/removed. +The third parameter is timeout value in usec. +:: + + pm_qos_update_target "action=%s prev_value=%d curr_value=%d" + pm_qos_update_flags "action=%s prev_value=0x%x curr_value=0x%x" + +The first parameter gives the QoS action name (e.g. "ADD_REQ"). +The second parameter is the previous QoS value. +The third parameter is the current QoS value to update. + +And, there are also events used for device PM QoS add/update/remove request. +:: + + dev_pm_qos_add_request "device=%s type=%s new_value=%d" + dev_pm_qos_update_request "device=%s type=%s new_value=%d" + dev_pm_qos_remove_request "device=%s type=%s new_value=%d" + +The first parameter gives the device name which tries to add/update/remove +QoS requests. +The second parameter gives the request type (e.g. "DEV_PM_QOS_RESUME_LATENCY"). +The third parameter is value to be added/updated/removed. diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst new file mode 100644 index 000000000..f7e1fcc09 --- /dev/null +++ b/Documentation/trace/events.rst @@ -0,0 +1,527 @@ +============= +Event Tracing +============= + +:Author: Theodore Ts'o +:Updated: Li Zefan and Tom Zanussi + +1. Introduction +=============== + +Tracepoints (see Documentation/trace/tracepoints.rst) can be used +without creating custom kernel modules to register probe functions +using the event tracing infrastructure. + +Not all tracepoints can be traced using the event tracing system; +the kernel developer must provide code snippets which define how the +tracing information is saved into the tracing buffer, and how the +tracing information should be printed. + +2. Using Event Tracing +====================== + +2.1 Via the 'set_event' interface +--------------------------------- + +The events which are available for tracing can be found in the file +/sys/kernel/debug/tracing/available_events. + +To enable a particular event, such as 'sched_wakeup', simply echo it +to /sys/kernel/debug/tracing/set_event. For example:: + + # echo sched_wakeup >> /sys/kernel/debug/tracing/set_event + +.. Note:: '>>' is necessary, otherwise it will firstly disable all the events. + +To disable an event, echo the event name to the set_event file prefixed +with an exclamation point:: + + # echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event + +To disable all events, echo an empty line to the set_event file:: + + # echo > /sys/kernel/debug/tracing/set_event + +To enable all events, echo ``*:*`` or ``*:`` to the set_event file:: + + # echo *:* > /sys/kernel/debug/tracing/set_event + +The events are organized into subsystems, such as ext4, irq, sched, +etc., and a full event name looks like this: <subsystem>:<event>. The +subsystem name is optional, but it is displayed in the available_events +file. All of the events in a subsystem can be specified via the syntax +``<subsystem>:*``; for example, to enable all irq events, you can use the +command:: + + # echo 'irq:*' > /sys/kernel/debug/tracing/set_event + +2.2 Via the 'enable' toggle +--------------------------- + +The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy +of directories. + +To enable event 'sched_wakeup':: + + # echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable + +To disable it:: + + # echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable + +To enable all events in sched subsystem:: + + # echo 1 > /sys/kernel/debug/tracing/events/sched/enable + +To enable all events:: + + # echo 1 > /sys/kernel/debug/tracing/events/enable + +When reading one of these enable files, there are four results: + + - 0 - all events this file affects are disabled + - 1 - all events this file affects are enabled + - X - there is a mixture of events enabled and disabled + - ? - this file does not affect any event + +2.3 Boot option +--------------- + +In order to facilitate early boot debugging, use boot option:: + + trace_event=[event-list] + +event-list is a comma separated list of events. See section 2.1 for event +format. + +3. Defining an event-enabled tracepoint +======================================= + +See The example provided in samples/trace_events + +4. Event formats +================ + +Each trace event has a 'format' file associated with it that contains +a description of each field in a logged event. This information can +be used to parse the binary trace stream, and is also the place to +find the field names that can be used in event filters (see section 5). + +It also displays the format string that will be used to print the +event in text mode, along with the event name and ID used for +profiling. + +Every event has a set of ``common`` fields associated with it; these are +the fields prefixed with ``common_``. The other fields vary between +events and correspond to the fields defined in the TRACE_EVENT +definition for that event. + +Each field in the format has the form:: + + field:field-type field-name; offset:N; size:N; + +where offset is the offset of the field in the trace record and size +is the size of the data item, in bytes. + +For example, here's the information displayed for the 'sched_wakeup' +event:: + + # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format + + name: sched_wakeup + ID: 60 + format: + field:unsigned short common_type; offset:0; size:2; + field:unsigned char common_flags; offset:2; size:1; + field:unsigned char common_preempt_count; offset:3; size:1; + field:int common_pid; offset:4; size:4; + field:int common_tgid; offset:8; size:4; + + field:char comm[TASK_COMM_LEN]; offset:12; size:16; + field:pid_t pid; offset:28; size:4; + field:int prio; offset:32; size:4; + field:int success; offset:36; size:4; + field:int cpu; offset:40; size:4; + + print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid, + REC->prio, REC->success, REC->cpu + +This event contains 10 fields, the first 5 common and the remaining 5 +event-specific. All the fields for this event are numeric, except for +'comm' which is a string, a distinction important for event filtering. + +5. Event filtering +================== + +Trace events can be filtered in the kernel by associating boolean +'filter expressions' with them. As soon as an event is logged into +the trace buffer, its fields are checked against the filter expression +associated with that event type. An event with field values that +'match' the filter will appear in the trace output, and an event whose +values don't match will be discarded. An event with no filter +associated with it matches everything, and is the default when no +filter has been set for an event. + +5.1 Expression syntax +--------------------- + +A filter expression consists of one or more 'predicates' that can be +combined using the logical operators '&&' and '||'. A predicate is +simply a clause that compares the value of a field contained within a +logged event with a constant value and returns either 0 or 1 depending +on whether the field value matched (1) or didn't match (0):: + + field-name relational-operator value + +Parentheses can be used to provide arbitrary logical groupings and +double-quotes can be used to prevent the shell from interpreting +operators as shell metacharacters. + +The field-names available for use in filters can be found in the +'format' files for trace events (see section 4). + +The relational-operators depend on the type of the field being tested: + +The operators available for numeric fields are: + +==, !=, <, <=, >, >=, & + +And for string fields they are: + +==, !=, ~ + +The glob (~) accepts a wild card character (\*,?) and character classes +([). For example:: + + prev_comm ~ "*sh" + prev_comm ~ "sh*" + prev_comm ~ "*sh*" + prev_comm ~ "ba*sh" + +5.2 Setting filters +------------------- + +A filter for an individual event is set by writing a filter expression +to the 'filter' file for the given event. + +For example:: + + # cd /sys/kernel/debug/tracing/events/sched/sched_wakeup + # echo "common_preempt_count > 4" > filter + +A slightly more involved example:: + + # cd /sys/kernel/debug/tracing/events/signal/signal_generate + # echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter + +If there is an error in the expression, you'll get an 'Invalid +argument' error when setting it, and the erroneous string along with +an error message can be seen by looking at the filter e.g.:: + + # cd /sys/kernel/debug/tracing/events/signal/signal_generate + # echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter + -bash: echo: write error: Invalid argument + # cat filter + ((sig >= 10 && sig < 15) || dsig == 17) && comm != bash + ^ + parse_error: Field not found + +Currently the caret ('^') for an error always appears at the beginning of +the filter string; the error message should still be useful though +even without more accurate position info. + +5.3 Clearing filters +-------------------- + +To clear the filter for an event, write a '0' to the event's filter +file. + +To clear the filters for all events in a subsystem, write a '0' to the +subsystem's filter file. + +5.3 Subsystem filters +--------------------- + +For convenience, filters for every event in a subsystem can be set or +cleared as a group by writing a filter expression into the filter file +at the root of the subsystem. Note however, that if a filter for any +event within the subsystem lacks a field specified in the subsystem +filter, or if the filter can't be applied for any other reason, the +filter for that event will retain its previous setting. This can +result in an unintended mixture of filters which could lead to +confusing (to the user who might think different filters are in +effect) trace output. Only filters that reference just the common +fields can be guaranteed to propagate successfully to all events. + +Here are a few subsystem filter examples that also illustrate the +above points: + +Clear the filters on all events in the sched subsystem:: + + # cd /sys/kernel/debug/tracing/events/sched + # echo 0 > filter + # cat sched_switch/filter + none + # cat sched_wakeup/filter + none + +Set a filter using only common fields for all events in the sched +subsystem (all events end up with the same filter):: + + # cd /sys/kernel/debug/tracing/events/sched + # echo common_pid == 0 > filter + # cat sched_switch/filter + common_pid == 0 + # cat sched_wakeup/filter + common_pid == 0 + +Attempt to set a filter using a non-common field for all events in the +sched subsystem (all events but those that have a prev_pid field retain +their old filters):: + + # cd /sys/kernel/debug/tracing/events/sched + # echo prev_pid == 0 > filter + # cat sched_switch/filter + prev_pid == 0 + # cat sched_wakeup/filter + common_pid == 0 + +5.4 PID filtering +----------------- + +The set_event_pid file in the same directory as the top events directory +exists, will filter all events from tracing any task that does not have the +PID listed in the set_event_pid file. +:: + + # cd /sys/kernel/debug/tracing + # echo $$ > set_event_pid + # echo 1 > events/enable + +Will only trace events for the current task. + +To add more PIDs without losing the PIDs already included, use '>>'. +:: + + # echo 123 244 1 >> set_event_pid + + +6. Event triggers +================= + +Trace events can be made to conditionally invoke trigger 'commands' +which can take various forms and are described in detail below; +examples would be enabling or disabling other trace events or invoking +a stack trace whenever the trace event is hit. Whenever a trace event +with attached triggers is invoked, the set of trigger commands +associated with that event is invoked. Any given trigger can +additionally have an event filter of the same form as described in +section 5 (Event filtering) associated with it - the command will only +be invoked if the event being invoked passes the associated filter. +If no filter is associated with the trigger, it always passes. + +Triggers are added to and removed from a particular event by writing +trigger expressions to the 'trigger' file for the given event. + +A given event can have any number of triggers associated with it, +subject to any restrictions that individual commands may have in that +regard. + +Event triggers are implemented on top of "soft" mode, which means that +whenever a trace event has one or more triggers associated with it, +the event is activated even if it isn't actually enabled, but is +disabled in a "soft" mode. That is, the tracepoint will be called, +but just will not be traced, unless of course it's actually enabled. +This scheme allows triggers to be invoked even for events that aren't +enabled, and also allows the current event filter implementation to be +used for conditionally invoking triggers. + +The syntax for event triggers is roughly based on the syntax for +set_ftrace_filter 'ftrace filter commands' (see the 'Filter commands' +section of Documentation/trace/ftrace.rst), but there are major +differences and the implementation isn't currently tied to it in any +way, so beware about making generalizations between the two. + +Note: Writing into trace_marker (See Documentation/trace/ftrace.rst) + can also enable triggers that are written into + /sys/kernel/tracing/events/ftrace/print/trigger + +6.1 Expression syntax +--------------------- + +Triggers are added by echoing the command to the 'trigger' file:: + + # echo 'command[:count] [if filter]' > trigger + +Triggers are removed by echoing the same command but starting with '!' +to the 'trigger' file:: + + # echo '!command[:count] [if filter]' > trigger + +The [if filter] part isn't used in matching commands when removing, so +leaving that off in a '!' command will accomplish the same thing as +having it in. + +The filter syntax is the same as that described in the 'Event +filtering' section above. + +For ease of use, writing to the trigger file using '>' currently just +adds or removes a single trigger and there's no explicit '>>' support +('>' actually behaves like '>>') or truncation support to remove all +triggers (you have to use '!' for each one added.) + +6.2 Supported trigger commands +------------------------------ + +The following commands are supported: + +- enable_event/disable_event + + These commands can enable or disable another trace event whenever + the triggering event is hit. When these commands are registered, + the other trace event is activated, but disabled in a "soft" mode. + That is, the tracepoint will be called, but just will not be traced. + The event tracepoint stays in this mode as long as there's a trigger + in effect that can trigger it. + + For example, the following trigger causes kmalloc events to be + traced when a read system call is entered, and the :1 at the end + specifies that this enablement happens only once:: + + # echo 'enable_event:kmem:kmalloc:1' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger + + The following trigger causes kmalloc events to stop being traced + when a read system call exits. This disablement happens on every + read system call exit:: + + # echo 'disable_event:kmem:kmalloc' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger + + The format is:: + + enable_event:<system>:<event>[:count] + disable_event:<system>:<event>[:count] + + To remove the above commands:: + + # echo '!enable_event:kmem:kmalloc:1' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger + + # echo '!disable_event:kmem:kmalloc' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger + + Note that there can be any number of enable/disable_event triggers + per triggering event, but there can only be one trigger per + triggered event. e.g. sys_enter_read can have triggers enabling both + kmem:kmalloc and sched:sched_switch, but can't have two kmem:kmalloc + versions such as kmem:kmalloc and kmem:kmalloc:1 or 'kmem:kmalloc if + bytes_req == 256' and 'kmem:kmalloc if bytes_alloc == 256' (they + could be combined into a single filter on kmem:kmalloc though). + +- stacktrace + + This command dumps a stacktrace in the trace buffer whenever the + triggering event occurs. + + For example, the following trigger dumps a stacktrace every time the + kmalloc tracepoint is hit:: + + # echo 'stacktrace' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + The following trigger dumps a stacktrace the first 5 times a kmalloc + request happens with a size >= 64K:: + + # echo 'stacktrace:5 if bytes_req >= 65536' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + The format is:: + + stacktrace[:count] + + To remove the above commands:: + + # echo '!stacktrace' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # echo '!stacktrace:5 if bytes_req >= 65536' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + The latter can also be removed more simply by the following (without + the filter):: + + # echo '!stacktrace:5' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + Note that there can be only one stacktrace trigger per triggering + event. + +- snapshot + + This command causes a snapshot to be triggered whenever the + triggering event occurs. + + The following command creates a snapshot every time a block request + queue is unplugged with a depth > 1. If you were tracing a set of + events or functions at the time, the snapshot trace buffer would + capture those events when the trigger event occurred:: + + # echo 'snapshot if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + To only snapshot once:: + + # echo 'snapshot:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + To remove the above commands:: + + # echo '!snapshot if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + # echo '!snapshot:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + Note that there can be only one snapshot trigger per triggering + event. + +- traceon/traceoff + + These commands turn tracing on and off when the specified events are + hit. The parameter determines how many times the tracing system is + turned on and off. If unspecified, there is no limit. + + The following command turns tracing off the first time a block + request queue is unplugged with a depth > 1. If you were tracing a + set of events or functions at the time, you could then examine the + trace buffer to see the sequence of events that led up to the + trigger event:: + + # echo 'traceoff:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + To always disable tracing when nr_rq > 1:: + + # echo 'traceoff if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + To remove the above commands:: + + # echo '!traceoff:1 if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + # echo '!traceoff if nr_rq > 1' > \ + /sys/kernel/debug/tracing/events/block/block_unplug/trigger + + Note that there can be only one traceon or traceoff trigger per + triggering event. + +- hist + + This command aggregates event hits into a hash table keyed on one or + more trace event format fields (or stacktrace) and a set of running + totals derived from one or more trace event format fields and/or + event counts (hitcount). + + See Documentation/trace/histogram.rst for details and examples. diff --git a/Documentation/trace/ftrace-design.rst b/Documentation/trace/ftrace-design.rst new file mode 100644 index 000000000..a8e22e0db --- /dev/null +++ b/Documentation/trace/ftrace-design.rst @@ -0,0 +1,419 @@ +====================== +Function Tracer Design +====================== + +:Author: Mike Frysinger + +.. caution:: + This document is out of date. Some of the description below doesn't + match current implementation now. + +Introduction +------------ + +Here we will cover the architecture pieces that the common function tracing +code relies on for proper functioning. Things are broken down into increasing +complexity so that you can start simple and at least get basic functionality. + +Note that this focuses on architecture implementation details only. If you +want more explanation of a feature in terms of common code, review the common +ftrace.txt file. + +Ideally, everyone who wishes to retain performance while supporting tracing in +their kernel should make it all the way to dynamic ftrace support. + + +Prerequisites +------------- + +Ftrace relies on these features being implemented: + - STACKTRACE_SUPPORT - implement save_stack_trace() + - TRACE_IRQFLAGS_SUPPORT - implement include/asm/irqflags.h + + +HAVE_FUNCTION_TRACER +-------------------- + +You will need to implement the mcount and the ftrace_stub functions. + +The exact mcount symbol name will depend on your toolchain. Some call it +"mcount", "_mcount", or even "__mcount". You can probably figure it out by +running something like:: + + $ echo 'main(){}' | gcc -x c -S -o - - -pg | grep mcount + call mcount + +We'll make the assumption below that the symbol is "mcount" just to keep things +nice and simple in the examples. + +Keep in mind that the ABI that is in effect inside of the mcount function is +*highly* architecture/toolchain specific. We cannot help you in this regard, +sorry. Dig up some old documentation and/or find someone more familiar than +you to bang ideas off of. Typically, register usage (argument/scratch/etc...) +is a major issue at this point, especially in relation to the location of the +mcount call (before/after function prologue). You might also want to look at +how glibc has implemented the mcount function for your architecture. It might +be (semi-)relevant. + +The mcount function should check the function pointer ftrace_trace_function +to see if it is set to ftrace_stub. If it is, there is nothing for you to do, +so return immediately. If it isn't, then call that function in the same way +the mcount function normally calls __mcount_internal -- the first argument is +the "frompc" while the second argument is the "selfpc" (adjusted to remove the +size of the mcount call that is embedded in the function). + +For example, if the function foo() calls bar(), when the bar() function calls +mcount(), the arguments mcount() will pass to the tracer are: + + - "frompc" - the address bar() will use to return to foo() + - "selfpc" - the address bar() (with mcount() size adjustment) + +Also keep in mind that this mcount function will be called *a lot*, so +optimizing for the default case of no tracer will help the smooth running of +your system when tracing is disabled. So the start of the mcount function is +typically the bare minimum with checking things before returning. That also +means the code flow should usually be kept linear (i.e. no branching in the nop +case). This is of course an optimization and not a hard requirement. + +Here is some pseudo code that should help (these functions should actually be +implemented in assembly):: + + void ftrace_stub(void) + { + return; + } + + void mcount(void) + { + /* save any bare state needed in order to do initial checking */ + + extern void (*ftrace_trace_function)(unsigned long, unsigned long); + if (ftrace_trace_function != ftrace_stub) + goto do_trace; + + /* restore any bare state */ + + return; + + do_trace: + + /* save all state needed by the ABI (see paragraph above) */ + + unsigned long frompc = ...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + ftrace_trace_function(frompc, selfpc); + + /* restore all state needed by the ABI */ + } + +Don't forget to export mcount for modules ! +:: + + extern void mcount(void); + EXPORT_SYMBOL(mcount); + + +HAVE_FUNCTION_GRAPH_TRACER +-------------------------- + +Deep breath ... time to do some real work. Here you will need to update the +mcount function to check ftrace graph function pointers, as well as implement +some functions to save (hijack) and restore the return address. + +The mcount function should check the function pointers ftrace_graph_return +(compare to ftrace_stub) and ftrace_graph_entry (compare to +ftrace_graph_entry_stub). If either of those is not set to the relevant stub +function, call the arch-specific function ftrace_graph_caller which in turn +calls the arch-specific function prepare_ftrace_return. Neither of these +function names is strictly required, but you should use them anyway to stay +consistent across the architecture ports -- easier to compare & contrast +things. + +The arguments to prepare_ftrace_return are slightly different than what are +passed to ftrace_trace_function. The second argument "selfpc" is the same, +but the first argument should be a pointer to the "frompc". Typically this is +located on the stack. This allows the function to hijack the return address +temporarily to have it point to the arch-specific function return_to_handler. +That function will simply call the common ftrace_return_to_handler function and +that will return the original return address with which you can return to the +original call site. + +Here is the updated mcount pseudo code:: + + void mcount(void) + { + ... + if (ftrace_trace_function != ftrace_stub) + goto do_trace; + + +#ifdef CONFIG_FUNCTION_GRAPH_TRACER + + extern void (*ftrace_graph_return)(...); + + extern void (*ftrace_graph_entry)(...); + + if (ftrace_graph_return != ftrace_stub || + + ftrace_graph_entry != ftrace_graph_entry_stub) + + ftrace_graph_caller(); + +#endif + + /* restore any bare state */ + ... + +Here is the pseudo code for the new ftrace_graph_caller assembly function:: + + #ifdef CONFIG_FUNCTION_GRAPH_TRACER + void ftrace_graph_caller(void) + { + /* save all state needed by the ABI */ + + unsigned long *frompc = &...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + /* passing frame pointer up is optional -- see below */ + prepare_ftrace_return(frompc, selfpc, frame_pointer); + + /* restore all state needed by the ABI */ + } + #endif + +For information on how to implement prepare_ftrace_return(), simply look at the +x86 version (the frame pointer passing is optional; see the next section for +more information). The only architecture-specific piece in it is the setup of +the fault recovery table (the asm(...) code). The rest should be the same +across architectures. + +Here is the pseudo code for the new return_to_handler assembly function. Note +that the ABI that applies here is different from what applies to the mcount +code. Since you are returning from a function (after the epilogue), you might +be able to skimp on things saved/restored (usually just registers used to pass +return values). +:: + + #ifdef CONFIG_FUNCTION_GRAPH_TRACER + void return_to_handler(void) + { + /* save all state needed by the ABI (see paragraph above) */ + + void (*original_return_point)(void) = ftrace_return_to_handler(); + + /* restore all state needed by the ABI */ + + /* this is usually either a return or a jump */ + original_return_point(); + } + #endif + + +HAVE_FUNCTION_GRAPH_FP_TEST +--------------------------- + +An arch may pass in a unique value (frame pointer) to both the entering and +exiting of a function. On exit, the value is compared and if it does not +match, then it will panic the kernel. This is largely a sanity check for bad +code generation with gcc. If gcc for your port sanely updates the frame +pointer under different optimization levels, then ignore this option. + +However, adding support for it isn't terribly difficult. In your assembly code +that calls prepare_ftrace_return(), pass the frame pointer as the 3rd argument. +Then in the C version of that function, do what the x86 port does and pass it +along to ftrace_push_return_trace() instead of a stub value of 0. + +Similarly, when you call ftrace_return_to_handler(), pass it the frame pointer. + +HAVE_FUNCTION_GRAPH_RET_ADDR_PTR +-------------------------------- + +An arch may pass in a pointer to the return address on the stack. This +prevents potential stack unwinding issues where the unwinder gets out of +sync with ret_stack and the wrong addresses are reported by +ftrace_graph_ret_addr(). + +Adding support for it is easy: just define the macro in asm/ftrace.h and +pass the return address pointer as the 'retp' argument to +ftrace_push_return_trace(). + +HAVE_FTRACE_NMI_ENTER +--------------------- + +If you can't trace NMI functions, then skip this option. + +<details to be filled> + + +HAVE_SYSCALL_TRACEPOINTS +------------------------ + +You need very few things to get the syscalls tracing in an arch. + + - Support HAVE_ARCH_TRACEHOOK (see arch/Kconfig). + - Have a NR_syscalls variable in <asm/unistd.h> that provides the number + of syscalls supported by the arch. + - Support the TIF_SYSCALL_TRACEPOINT thread flags. + - Put the trace_sys_enter() and trace_sys_exit() tracepoints calls from ptrace + in the ptrace syscalls tracing path. + - If the system call table on this arch is more complicated than a simple array + of addresses of the system calls, implement an arch_syscall_addr to return + the address of a given system call. + - If the symbol names of the system calls do not match the function names on + this arch, define ARCH_HAS_SYSCALL_MATCH_SYM_NAME in asm/ftrace.h and + implement arch_syscall_match_sym_name with the appropriate logic to return + true if the function name corresponds with the symbol name. + - Tag this arch as HAVE_SYSCALL_TRACEPOINTS. + + +HAVE_FTRACE_MCOUNT_RECORD +------------------------- + +See scripts/recordmcount.pl for more info. Just fill in the arch-specific +details for how to locate the addresses of mcount call sites via objdump. +This option doesn't make much sense without also implementing dynamic ftrace. + + +HAVE_DYNAMIC_FTRACE +------------------- + +You will first need HAVE_FTRACE_MCOUNT_RECORD and HAVE_FUNCTION_TRACER, so +scroll your reader back up if you got over eager. + +Once those are out of the way, you will need to implement: + - asm/ftrace.h: + - MCOUNT_ADDR + - ftrace_call_adjust() + - struct dyn_arch_ftrace{} + - asm code: + - mcount() (new stub) + - ftrace_caller() + - ftrace_call() + - ftrace_stub() + - C code: + - ftrace_dyn_arch_init() + - ftrace_make_nop() + - ftrace_make_call() + - ftrace_update_ftrace_func() + +First you will need to fill out some arch details in your asm/ftrace.h. + +Define MCOUNT_ADDR as the address of your mcount symbol similar to:: + + #define MCOUNT_ADDR ((unsigned long)mcount) + +Since no one else will have a decl for that function, you will need to:: + + extern void mcount(void); + +You will also need the helper function ftrace_call_adjust(). Most people +will be able to stub it out like so:: + + static inline unsigned long ftrace_call_adjust(unsigned long addr) + { + return addr; + } + +<details to be filled> + +Lastly you will need the custom dyn_arch_ftrace structure. If you need +some extra state when runtime patching arbitrary call sites, this is the +place. For now though, create an empty struct:: + + struct dyn_arch_ftrace { + /* No extra data needed */ + }; + +With the header out of the way, we can fill out the assembly code. While we +did already create a mcount() function earlier, dynamic ftrace only wants a +stub function. This is because the mcount() will only be used during boot +and then all references to it will be patched out never to return. Instead, +the guts of the old mcount() will be used to create a new ftrace_caller() +function. Because the two are hard to merge, it will most likely be a lot +easier to have two separate definitions split up by #ifdefs. Same goes for +the ftrace_stub() as that will now be inlined in ftrace_caller(). + +Before we get confused anymore, let's check out some pseudo code so you can +implement your own stuff in assembly:: + + void mcount(void) + { + return; + } + + void ftrace_caller(void) + { + /* save all state needed by the ABI (see paragraph above) */ + + unsigned long frompc = ...; + unsigned long selfpc = <return address> - MCOUNT_INSN_SIZE; + + ftrace_call: + ftrace_stub(frompc, selfpc); + + /* restore all state needed by the ABI */ + + ftrace_stub: + return; + } + +This might look a little odd at first, but keep in mind that we will be runtime +patching multiple things. First, only functions that we actually want to trace +will be patched to call ftrace_caller(). Second, since we only have one tracer +active at a time, we will patch the ftrace_caller() function itself to call the +specific tracer in question. That is the point of the ftrace_call label. + +With that in mind, let's move on to the C code that will actually be doing the +runtime patching. You'll need a little knowledge of your arch's opcodes in +order to make it through the next section. + +Every arch has an init callback function. If you need to do something early on +to initialize some state, this is the time to do that. Otherwise, this simple +function below should be sufficient for most people:: + + int __init ftrace_dyn_arch_init(void) + { + return 0; + } + +There are two functions that are used to do runtime patching of arbitrary +functions. The first is used to turn the mcount call site into a nop (which +is what helps us retain runtime performance when not tracing). The second is +used to turn the mcount call site into a call to an arbitrary location (but +typically that is ftracer_caller()). See the general function definition in +linux/ftrace.h for the functions:: + + ftrace_make_nop() + ftrace_make_call() + +The rec->ip value is the address of the mcount call site that was collected +by the scripts/recordmcount.pl during build time. + +The last function is used to do runtime patching of the active tracer. This +will be modifying the assembly code at the location of the ftrace_call symbol +inside of the ftrace_caller() function. So you should have sufficient padding +at that location to support the new function calls you'll be inserting. Some +people will be using a "call" type instruction while others will be using a +"branch" type instruction. Specifically, the function is:: + + ftrace_update_ftrace_func() + + +HAVE_DYNAMIC_FTRACE + HAVE_FUNCTION_GRAPH_TRACER +------------------------------------------------ + +The function grapher needs a few tweaks in order to work with dynamic ftrace. +Basically, you will need to: + + - update: + - ftrace_caller() + - ftrace_graph_call() + - ftrace_graph_caller() + - implement: + - ftrace_enable_ftrace_graph_caller() + - ftrace_disable_ftrace_graph_caller() + +<details to be filled> + +Quick notes: + + - add a nop stub after the ftrace_call location named ftrace_graph_call; + stub needs to be large enough to support a call to ftrace_graph_caller() + - update ftrace_graph_caller() to work with being called by the new + ftrace_caller() since some semantics may have changed + - ftrace_enable_ftrace_graph_caller() will runtime patch the + ftrace_graph_call location with a call to ftrace_graph_caller() + - ftrace_disable_ftrace_graph_caller() will runtime patch the + ftrace_graph_call location with nops diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst new file mode 100644 index 000000000..1fbc69894 --- /dev/null +++ b/Documentation/trace/ftrace-uses.rst @@ -0,0 +1,294 @@ +================================= +Using ftrace to hook to functions +================================= + +.. Copyright 2017 VMware Inc. +.. Author: Steven Rostedt <srostedt@goodmis.org> +.. License: The GNU Free Documentation License, Version 1.2 +.. (dual licensed under the GPL v2) + +Written for: 4.14 + +Introduction +============ + +The ftrace infrastructure was originally created to attach callbacks to the +beginning of functions in order to record and trace the flow of the kernel. +But callbacks to the start of a function can have other use cases. Either +for live kernel patching, or for security monitoring. This document describes +how to use ftrace to implement your own function callbacks. + + +The ftrace context +================== +.. warning:: + + The ability to add a callback to almost any function within the + kernel comes with risks. A callback can be called from any context + (normal, softirq, irq, and NMI). Callbacks can also be called just before + going to idle, during CPU bring up and takedown, or going to user space. + This requires extra care to what can be done inside a callback. A callback + can be called outside the protective scope of RCU. + +The ftrace infrastructure has some protections against recursions and RCU +but one must still be very careful how they use the callbacks. + + +The ftrace_ops structure +======================== + +To register a function callback, a ftrace_ops is required. This structure +is used to tell ftrace what function should be called as the callback +as well as what protections the callback will perform and not require +ftrace to handle. + +There is only one field that is needed to be set when registering +an ftrace_ops with ftrace: + +.. code-block:: c + + struct ftrace_ops ops = { + .func = my_callback_func, + .flags = MY_FTRACE_FLAGS + .private = any_private_data_structure, + }; + +Both .flags and .private are optional. Only .func is required. + +To enable tracing call: + +.. c:function:: register_ftrace_function(&ops); + +To disable tracing call: + +.. c:function:: unregister_ftrace_function(&ops); + +The above is defined by including the header: + +.. c:function:: #include <linux/ftrace.h> + +The registered callback will start being called some time after the +register_ftrace_function() is called and before it returns. The exact time +that callbacks start being called is dependent upon architecture and scheduling +of services. The callback itself will have to handle any synchronization if it +must begin at an exact moment. + +The unregister_ftrace_function() will guarantee that the callback is +no longer being called by functions after the unregister_ftrace_function() +returns. Note that to perform this guarantee, the unregister_ftrace_function() +may take some time to finish. + + +The callback function +===================== + +The prototype of the callback function is as follows (as of v4.14): + +.. code-block:: c + + void callback_func(unsigned long ip, unsigned long parent_ip, + struct ftrace_ops *op, struct pt_regs *regs); + +@ip + This is the instruction pointer of the function that is being traced. + (where the fentry or mcount is within the function) + +@parent_ip + This is the instruction pointer of the function that called the + the function being traced (where the call of the function occurred). + +@op + This is a pointer to ftrace_ops that was used to register the callback. + This can be used to pass data to the callback via the private pointer. + +@regs + If the FTRACE_OPS_FL_SAVE_REGS or FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED + flags are set in the ftrace_ops structure, then this will be pointing + to the pt_regs structure like it would be if an breakpoint was placed + at the start of the function where ftrace was tracing. Otherwise it + either contains garbage, or NULL. + + +The ftrace FLAGS +================ + +The ftrace_ops flags are all defined and documented in include/linux/ftrace.h. +Some of the flags are used for internal infrastructure of ftrace, but the +ones that users should be aware of are the following: + +FTRACE_OPS_FL_SAVE_REGS + If the callback requires reading or modifying the pt_regs + passed to the callback, then it must set this flag. Registering + a ftrace_ops with this flag set on an architecture that does not + support passing of pt_regs to the callback will fail. + +FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED + Similar to SAVE_REGS but the registering of a + ftrace_ops on an architecture that does not support passing of regs + will not fail with this flag set. But the callback must check if + regs is NULL or not to determine if the architecture supports it. + +FTRACE_OPS_FL_RECURSION_SAFE + By default, a wrapper is added around the callback to + make sure that recursion of the function does not occur. That is, + if a function that is called as a result of the callback's execution + is also traced, ftrace will prevent the callback from being called + again. But this wrapper adds some overhead, and if the callback is + safe from recursion, it can set this flag to disable the ftrace + protection. + + Note, if this flag is set, and recursion does occur, it could cause + the system to crash, and possibly reboot via a triple fault. + + It is OK if another callback traces a function that is called by a + callback that is marked recursion safe. Recursion safe callbacks + must never trace any function that are called by the callback + itself or any nested functions that those functions call. + + If this flag is set, it is possible that the callback will also + be called with preemption enabled (when CONFIG_PREEMPT is set), + but this is not guaranteed. + +FTRACE_OPS_FL_IPMODIFY + Requires FTRACE_OPS_FL_SAVE_REGS set. If the callback is to "hijack" + the traced function (have another function called instead of the + traced function), it requires setting this flag. This is what live + kernel patches uses. Without this flag the pt_regs->ip can not be + modified. + + Note, only one ftrace_ops with FTRACE_OPS_FL_IPMODIFY set may be + registered to any given function at a time. + +FTRACE_OPS_FL_RCU + If this is set, then the callback will only be called by functions + where RCU is "watching". This is required if the callback function + performs any rcu_read_lock() operation. + + RCU stops watching when the system goes idle, the time when a CPU + is taken down and comes back online, and when entering from kernel + to user space and back to kernel space. During these transitions, + a callback may be executed and RCU synchronization will not protect + it. + + +Filtering which functions to trace +================================== + +If a callback is only to be called from specific functions, a filter must be +set up. The filters are added by name, or ip if it is known. + +.. code-block:: c + + int ftrace_set_filter(struct ftrace_ops *ops, unsigned char *buf, + int len, int reset); + +@ops + The ops to set the filter with + +@buf + The string that holds the function filter text. +@len + The length of the string. + +@reset + Non-zero to reset all filters before applying this filter. + +Filters denote which functions should be enabled when tracing is enabled. +If @buf is NULL and reset is set, all functions will be enabled for tracing. + +The @buf can also be a glob expression to enable all functions that +match a specific pattern. + +See Filter Commands in :file:`Documentation/trace/ftrace.rst`. + +To just trace the schedule function: + +.. code-block:: c + + ret = ftrace_set_filter(&ops, "schedule", strlen("schedule"), 0); + +To add more functions, call the ftrace_set_filter() more than once with the +@reset parameter set to zero. To remove the current filter set and replace it +with new functions defined by @buf, have @reset be non-zero. + +To remove all the filtered functions and trace all functions: + +.. code-block:: c + + ret = ftrace_set_filter(&ops, NULL, 0, 1); + + +Sometimes more than one function has the same name. To trace just a specific +function in this case, ftrace_set_filter_ip() can be used. + +.. code-block:: c + + ret = ftrace_set_filter_ip(&ops, ip, 0, 0); + +Although the ip must be the address where the call to fentry or mcount is +located in the function. This function is used by perf and kprobes that +gets the ip address from the user (usually using debug info from the kernel). + +If a glob is used to set the filter, functions can be added to a "notrace" +list that will prevent those functions from calling the callback. +The "notrace" list takes precedence over the "filter" list. If the +two lists are non-empty and contain the same functions, the callback will not +be called by any function. + +An empty "notrace" list means to allow all functions defined by the filter +to be traced. + +.. code-block:: c + + int ftrace_set_notrace(struct ftrace_ops *ops, unsigned char *buf, + int len, int reset); + +This takes the same parameters as ftrace_set_filter() but will add the +functions it finds to not be traced. This is a separate list from the +filter list, and this function does not modify the filter list. + +A non-zero @reset will clear the "notrace" list before adding functions +that match @buf to it. + +Clearing the "notrace" list is the same as clearing the filter list + +.. code-block:: c + + ret = ftrace_set_notrace(&ops, NULL, 0, 1); + +The filter and notrace lists may be changed at any time. If only a set of +functions should call the callback, it is best to set the filters before +registering the callback. But the changes may also happen after the callback +has been registered. + +If a filter is in place, and the @reset is non-zero, and @buf contains a +matching glob to functions, the switch will happen during the time of +the ftrace_set_filter() call. At no time will all functions call the callback. + +.. code-block:: c + + ftrace_set_filter(&ops, "schedule", strlen("schedule"), 1); + + register_ftrace_function(&ops); + + msleep(10); + + ftrace_set_filter(&ops, "try_to_wake_up", strlen("try_to_wake_up"), 1); + +is not the same as: + +.. code-block:: c + + ftrace_set_filter(&ops, "schedule", strlen("schedule"), 1); + + register_ftrace_function(&ops); + + msleep(10); + + ftrace_set_filter(&ops, NULL, 0, 1); + + ftrace_set_filter(&ops, "try_to_wake_up", strlen("try_to_wake_up"), 0); + +As the latter will have a short time where all functions will call +the callback, between the time of the reset, and the time of the +new setting of the filter. diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst new file mode 100644 index 000000000..7ea16a0ce --- /dev/null +++ b/Documentation/trace/ftrace.rst @@ -0,0 +1,3366 @@ +======================== +ftrace - Function Tracer +======================== + +Copyright 2008 Red Hat Inc. + +:Author: Steven Rostedt <srostedt@redhat.com> +:License: The GNU Free Documentation License, Version 1.2 + (dual licensed under the GPL v2) +:Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, + John Kacur, and David Teigland. + +- Written for: 2.6.28-rc2 +- Updated for: 3.10 +- Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt +- Converted to rst format - Changbin Du <changbin.du@intel.com> + +Introduction +------------ + +Ftrace is an internal tracer designed to help out developers and +designers of systems to find what is going on inside the kernel. +It can be used for debugging or analyzing latencies and +performance issues that take place outside of user-space. + +Although ftrace is typically considered the function tracer, it +is really a frame work of several assorted tracing utilities. +There's latency tracing to examine what occurs between interrupts +disabled and enabled, as well as for preemption and from a time +a task is woken to the task is actually scheduled in. + +One of the most common uses of ftrace is the event tracing. +Through out the kernel is hundreds of static event points that +can be enabled via the tracefs file system to see what is +going on in certain parts of the kernel. + +See events.txt for more information. + + +Implementation Details +---------------------- + +See :doc:`ftrace-design` for details for arch porters and such. + + +The File System +--------------- + +Ftrace uses the tracefs file system to hold the control files as +well as the files to display output. + +When tracefs is configured into the kernel (which selecting any ftrace +option will do) the directory /sys/kernel/tracing will be created. To mount +this directory, you can add to your /etc/fstab file:: + + tracefs /sys/kernel/tracing tracefs defaults 0 0 + +Or you can mount it at run time with:: + + mount -t tracefs nodev /sys/kernel/tracing + +For quicker access to that directory you may want to make a soft link to +it:: + + ln -s /sys/kernel/tracing /tracing + +.. attention:: + + Before 4.1, all ftrace tracing control files were within the debugfs + file system, which is typically located at /sys/kernel/debug/tracing. + For backward compatibility, when mounting the debugfs file system, + the tracefs file system will be automatically mounted at: + + /sys/kernel/debug/tracing + + All files located in the tracefs file system will be located in that + debugfs file system directory as well. + +.. attention:: + + Any selected ftrace option will also create the tracefs file system. + The rest of the document will assume that you are in the ftrace directory + (cd /sys/kernel/tracing) and will only concentrate on the files within that + directory and not distract from the content with the extended + "/sys/kernel/tracing" path name. + +That's it! (assuming that you have ftrace configured into your kernel) + +After mounting tracefs you will have access to the control and output files +of ftrace. Here is a list of some of the key files: + + + Note: all time values are in microseconds. + + current_tracer: + + This is used to set or display the current tracer + that is configured. + + available_tracers: + + This holds the different types of tracers that + have been compiled into the kernel. The + tracers listed here can be configured by + echoing their name into current_tracer. + + tracing_on: + + This sets or displays whether writing to the trace + ring buffer is enabled. Echo 0 into this file to disable + the tracer or 1 to enable it. Note, this only disables + writing to the ring buffer, the tracing overhead may + still be occurring. + + The kernel function tracing_off() can be used within the + kernel to disable writing to the ring buffer, which will + set this file to "0". User space can re-enable tracing by + echoing "1" into the file. + + Note, the function and event trigger "traceoff" will also + set this file to zero and stop tracing. Which can also + be re-enabled by user space using this file. + + trace: + + This file holds the output of the trace in a human + readable format (described below). Note, tracing is temporarily + disabled while this file is being read (opened). + + trace_pipe: + + The output is the same as the "trace" file but this + file is meant to be streamed with live tracing. + Reads from this file will block until new data is + retrieved. Unlike the "trace" file, this file is a + consumer. This means reading from this file causes + sequential reads to display more current data. Once + data is read from this file, it is consumed, and + will not be read again with a sequential read. The + "trace" file is static, and if the tracer is not + adding more data, it will display the same + information every time it is read. This file will not + disable tracing while being read. + + trace_options: + + This file lets the user control the amount of data + that is displayed in one of the above output + files. Options also exist to modify how a tracer + or events work (stack traces, timestamps, etc). + + options: + + This is a directory that has a file for every available + trace option (also in trace_options). Options may also be set + or cleared by writing a "1" or "0" respectively into the + corresponding file with the option name. + + tracing_max_latency: + + Some of the tracers record the max latency. + For example, the maximum time that interrupts are disabled. + The maximum time is saved in this file. The max trace will also be + stored, and displayed by "trace". A new max trace will only be + recorded if the latency is greater than the value in this file + (in microseconds). + + By echoing in a time into this file, no latency will be recorded + unless it is greater than the time in this file. + + tracing_thresh: + + Some latency tracers will record a trace whenever the + latency is greater than the number in this file. + Only active when the file contains a number greater than 0. + (in microseconds) + + buffer_size_kb: + + This sets or displays the number of kilobytes each CPU + buffer holds. By default, the trace buffers are the same size + for each CPU. The displayed number is the size of the + CPU buffer and not total size of all buffers. The + trace buffers are allocated in pages (blocks of memory + that the kernel uses for allocation, usually 4 KB in size). + If the last page allocated has room for more bytes + than requested, the rest of the page will be used, + making the actual allocation bigger than requested or shown. + ( Note, the size may not be a multiple of the page size + due to buffer management meta-data. ) + + Buffer sizes for individual CPUs may vary + (see "per_cpu/cpu0/buffer_size_kb" below), and if they do + this file will show "X". + + buffer_total_size_kb: + + This displays the total combined size of all the trace buffers. + + free_buffer: + + If a process is performing tracing, and the ring buffer should be + shrunk "freed" when the process is finished, even if it were to be + killed by a signal, this file can be used for that purpose. On close + of this file, the ring buffer will be resized to its minimum size. + Having a process that is tracing also open this file, when the process + exits its file descriptor for this file will be closed, and in doing so, + the ring buffer will be "freed". + + It may also stop tracing if disable_on_free option is set. + + tracing_cpumask: + + This is a mask that lets the user only trace on specified CPUs. + The format is a hex string representing the CPUs. + + set_ftrace_filter: + + When dynamic ftrace is configured in (see the + section below "dynamic ftrace"), the code is dynamically + modified (code text rewrite) to disable calling of the + function profiler (mcount). This lets tracing be configured + in with practically no overhead in performance. This also + has a side effect of enabling or disabling specific functions + to be traced. Echoing names of functions into this file + will limit the trace to only those functions. + This influences the tracers "function" and "function_graph" + and thus also function profiling (see "function_profile_enabled"). + + The functions listed in "available_filter_functions" are what + can be written into this file. + + This interface also allows for commands to be used. See the + "Filter commands" section for more details. + + set_ftrace_notrace: + + This has an effect opposite to that of + set_ftrace_filter. Any function that is added here will not + be traced. If a function exists in both set_ftrace_filter + and set_ftrace_notrace, the function will _not_ be traced. + + set_ftrace_pid: + + Have the function tracer only trace the threads whose PID are + listed in this file. + + If the "function-fork" option is set, then when a task whose + PID is listed in this file forks, the child's PID will + automatically be added to this file, and the child will be + traced by the function tracer as well. This option will also + cause PIDs of tasks that exit to be removed from the file. + + set_event_pid: + + Have the events only trace a task with a PID listed in this file. + Note, sched_switch and sched_wake_up will also trace events + listed in this file. + + To have the PIDs of children of tasks with their PID in this file + added on fork, enable the "event-fork" option. That option will also + cause the PIDs of tasks to be removed from this file when the task + exits. + + set_graph_function: + + Functions listed in this file will cause the function graph + tracer to only trace these functions and the functions that + they call. (See the section "dynamic ftrace" for more details). + Note, set_ftrace_filter and set_ftrace_notrace still affects + what functions are being traced. + + set_graph_notrace: + + Similar to set_graph_function, but will disable function graph + tracing when the function is hit until it exits the function. + This makes it possible to ignore tracing functions that are called + by a specific function. + + available_filter_functions: + + This lists the functions that ftrace has processed and can trace. + These are the function names that you can pass to + "set_ftrace_filter", "set_ftrace_notrace", + "set_graph_function", or "set_graph_notrace". + (See the section "dynamic ftrace" below for more details.) + + dyn_ftrace_total_info: + + This file is for debugging purposes. The number of functions that + have been converted to nops and are available to be traced. + + enabled_functions: + + This file is more for debugging ftrace, but can also be useful + in seeing if any function has a callback attached to it. + Not only does the trace infrastructure use ftrace function + trace utility, but other subsystems might too. This file + displays all functions that have a callback attached to them + as well as the number of callbacks that have been attached. + Note, a callback may also call multiple functions which will + not be listed in this count. + + If the callback registered to be traced by a function with + the "save regs" attribute (thus even more overhead), a 'R' + will be displayed on the same line as the function that + is returning registers. + + If the callback registered to be traced by a function with + the "ip modify" attribute (thus the regs->ip can be changed), + an 'I' will be displayed on the same line as the function that + can be overridden. + + If the architecture supports it, it will also show what callback + is being directly called by the function. If the count is greater + than 1 it most likely will be ftrace_ops_list_func(). + + If the callback of the function jumps to a trampoline that is + specific to a the callback and not the standard trampoline, + its address will be printed as well as the function that the + trampoline calls. + + function_profile_enabled: + + When set it will enable all functions with either the function + tracer, or if configured, the function graph tracer. It will + keep a histogram of the number of functions that were called + and if the function graph tracer was configured, it will also keep + track of the time spent in those functions. The histogram + content can be displayed in the files: + + trace_stat/function<cpu> ( function0, function1, etc). + + trace_stat: + + A directory that holds different tracing stats. + + kprobe_events: + + Enable dynamic trace points. See kprobetrace.txt. + + kprobe_profile: + + Dynamic trace points stats. See kprobetrace.txt. + + max_graph_depth: + + Used with the function graph tracer. This is the max depth + it will trace into a function. Setting this to a value of + one will show only the first kernel function that is called + from user space. + + printk_formats: + + This is for tools that read the raw format files. If an event in + the ring buffer references a string, only a pointer to the string + is recorded into the buffer and not the string itself. This prevents + tools from knowing what that string was. This file displays the string + and address for the string allowing tools to map the pointers to what + the strings were. + + saved_cmdlines: + + Only the pid of the task is recorded in a trace event unless + the event specifically saves the task comm as well. Ftrace + makes a cache of pid mappings to comms to try to display + comms for events. If a pid for a comm is not listed, then + "<...>" is displayed in the output. + + If the option "record-cmd" is set to "0", then comms of tasks + will not be saved during recording. By default, it is enabled. + + saved_cmdlines_size: + + By default, 128 comms are saved (see "saved_cmdlines" above). To + increase or decrease the amount of comms that are cached, echo + in a the number of comms to cache, into this file. + + saved_tgids: + + If the option "record-tgid" is set, on each scheduling context switch + the Task Group ID of a task is saved in a table mapping the PID of + the thread to its TGID. By default, the "record-tgid" option is + disabled. + + snapshot: + + This displays the "snapshot" buffer and also lets the user + take a snapshot of the current running trace. + See the "Snapshot" section below for more details. + + stack_max_size: + + When the stack tracer is activated, this will display the + maximum stack size it has encountered. + See the "Stack Trace" section below. + + stack_trace: + + This displays the stack back trace of the largest stack + that was encountered when the stack tracer is activated. + See the "Stack Trace" section below. + + stack_trace_filter: + + This is similar to "set_ftrace_filter" but it limits what + functions the stack tracer will check. + + trace_clock: + + Whenever an event is recorded into the ring buffer, a + "timestamp" is added. This stamp comes from a specified + clock. By default, ftrace uses the "local" clock. This + clock is very fast and strictly per cpu, but on some + systems it may not be monotonic with respect to other + CPUs. In other words, the local clocks may not be in sync + with local clocks on other CPUs. + + Usual clocks for tracing:: + + # cat trace_clock + [local] global counter x86-tsc + + The clock with the square brackets around it is the one in effect. + + local: + Default clock, but may not be in sync across CPUs + + global: + This clock is in sync with all CPUs but may + be a bit slower than the local clock. + + counter: + This is not a clock at all, but literally an atomic + counter. It counts up one by one, but is in sync + with all CPUs. This is useful when you need to + know exactly the order events occurred with respect to + each other on different CPUs. + + uptime: + This uses the jiffies counter and the time stamp + is relative to the time since boot up. + + perf: + This makes ftrace use the same clock that perf uses. + Eventually perf will be able to read ftrace buffers + and this will help out in interleaving the data. + + x86-tsc: + Architectures may define their own clocks. For + example, x86 uses its own TSC cycle clock here. + + ppc-tb: + This uses the powerpc timebase register value. + This is in sync across CPUs and can also be used + to correlate events across hypervisor/guest if + tb_offset is known. + + mono: + This uses the fast monotonic clock (CLOCK_MONOTONIC) + which is monotonic and is subject to NTP rate adjustments. + + mono_raw: + This is the raw monotonic clock (CLOCK_MONOTONIC_RAW) + which is montonic but is not subject to any rate adjustments + and ticks at the same rate as the hardware clocksource. + + boot: + This is the boot clock (CLOCK_BOOTTIME) and is based on the + fast monotonic clock, but also accounts for time spent in + suspend. Since the clock access is designed for use in + tracing in the suspend path, some side effects are possible + if clock is accessed after the suspend time is accounted before + the fast mono clock is updated. In this case, the clock update + appears to happen slightly sooner than it normally would have. + Also on 32-bit systems, it's possible that the 64-bit boot offset + sees a partial update. These effects are rare and post + processing should be able to handle them. See comments in the + ktime_get_boot_fast_ns() function for more information. + + To set a clock, simply echo the clock name into this file:: + + # echo global > trace_clock + + trace_marker: + + This is a very useful file for synchronizing user space + with events happening in the kernel. Writing strings into + this file will be written into the ftrace buffer. + + It is useful in applications to open this file at the start + of the application and just reference the file descriptor + for the file:: + + void trace_write(const char *fmt, ...) + { + va_list ap; + char buf[256]; + int n; + + if (trace_fd < 0) + return; + + va_start(ap, fmt); + n = vsnprintf(buf, 256, fmt, ap); + va_end(ap); + + write(trace_fd, buf, n); + } + + start:: + + trace_fd = open("trace_marker", WR_ONLY); + + Note: Writing into the trace_marker file can also initiate triggers + that are written into /sys/kernel/tracing/events/ftrace/print/trigger + See "Event triggers" in Documentation/trace/events.rst and an + example in Documentation/trace/histogram.rst (Section 3.) + + trace_marker_raw: + + This is similar to trace_marker above, but is meant for for binary data + to be written to it, where a tool can be used to parse the data + from trace_pipe_raw. + + uprobe_events: + + Add dynamic tracepoints in programs. + See uprobetracer.txt + + uprobe_profile: + + Uprobe statistics. See uprobetrace.txt + + instances: + + This is a way to make multiple trace buffers where different + events can be recorded in different buffers. + See "Instances" section below. + + events: + + This is the trace event directory. It holds event tracepoints + (also known as static tracepoints) that have been compiled + into the kernel. It shows what event tracepoints exist + and how they are grouped by system. There are "enable" + files at various levels that can enable the tracepoints + when a "1" is written to them. + + See events.txt for more information. + + set_event: + + By echoing in the event into this file, will enable that event. + + See events.txt for more information. + + available_events: + + A list of events that can be enabled in tracing. + + See events.txt for more information. + + timestamp_mode: + + Certain tracers may change the timestamp mode used when + logging trace events into the event buffer. Events with + different modes can coexist within a buffer but the mode in + effect when an event is logged determines which timestamp mode + is used for that event. The default timestamp mode is + 'delta'. + + Usual timestamp modes for tracing: + + # cat timestamp_mode + [delta] absolute + + The timestamp mode with the square brackets around it is the + one in effect. + + delta: Default timestamp mode - timestamp is a delta against + a per-buffer timestamp. + + absolute: The timestamp is a full timestamp, not a delta + against some other value. As such it takes up more + space and is less efficient. + + hwlat_detector: + + Directory for the Hardware Latency Detector. + See "Hardware Latency Detector" section below. + + per_cpu: + + This is a directory that contains the trace per_cpu information. + + per_cpu/cpu0/buffer_size_kb: + + The ftrace buffer is defined per_cpu. That is, there's a separate + buffer for each CPU to allow writes to be done atomically, + and free from cache bouncing. These buffers may have different + size buffers. This file is similar to the buffer_size_kb + file, but it only displays or sets the buffer size for the + specific CPU. (here cpu0). + + per_cpu/cpu0/trace: + + This is similar to the "trace" file, but it will only display + the data specific for the CPU. If written to, it only clears + the specific CPU buffer. + + per_cpu/cpu0/trace_pipe + + This is similar to the "trace_pipe" file, and is a consuming + read, but it will only display (and consume) the data specific + for the CPU. + + per_cpu/cpu0/trace_pipe_raw + + For tools that can parse the ftrace ring buffer binary format, + the trace_pipe_raw file can be used to extract the data + from the ring buffer directly. With the use of the splice() + system call, the buffer data can be quickly transferred to + a file or to the network where a server is collecting the + data. + + Like trace_pipe, this is a consuming reader, where multiple + reads will always produce different data. + + per_cpu/cpu0/snapshot: + + This is similar to the main "snapshot" file, but will only + snapshot the current CPU (if supported). It only displays + the content of the snapshot for a given CPU, and if + written to, only clears this CPU buffer. + + per_cpu/cpu0/snapshot_raw: + + Similar to the trace_pipe_raw, but will read the binary format + from the snapshot buffer for the given CPU. + + per_cpu/cpu0/stats: + + This displays certain stats about the ring buffer: + + entries: + The number of events that are still in the buffer. + + overrun: + The number of lost events due to overwriting when + the buffer was full. + + commit overrun: + Should always be zero. + This gets set if so many events happened within a nested + event (ring buffer is re-entrant), that it fills the + buffer and starts dropping events. + + bytes: + Bytes actually read (not overwritten). + + oldest event ts: + The oldest timestamp in the buffer + + now ts: + The current timestamp + + dropped events: + Events lost due to overwrite option being off. + + read events: + The number of events read. + +The Tracers +----------- + +Here is the list of current tracers that may be configured. + + "function" + + Function call tracer to trace all kernel functions. + + "function_graph" + + Similar to the function tracer except that the + function tracer probes the functions on their entry + whereas the function graph tracer traces on both entry + and exit of the functions. It then provides the ability + to draw a graph of function calls similar to C code + source. + + "blk" + + The block tracer. The tracer used by the blktrace user + application. + + "hwlat" + + The Hardware Latency tracer is used to detect if the hardware + produces any latency. See "Hardware Latency Detector" section + below. + + "irqsoff" + + Traces the areas that disable interrupts and saves + the trace with the longest max latency. + See tracing_max_latency. When a new max is recorded, + it replaces the old trace. It is best to view this + trace with the latency-format option enabled, which + happens automatically when the tracer is selected. + + "preemptoff" + + Similar to irqsoff but traces and records the amount of + time for which preemption is disabled. + + "preemptirqsoff" + + Similar to irqsoff and preemptoff, but traces and + records the largest time for which irqs and/or preemption + is disabled. + + "wakeup" + + Traces and records the max latency that it takes for + the highest priority task to get scheduled after + it has been woken up. + Traces all tasks as an average developer would expect. + + "wakeup_rt" + + Traces and records the max latency that it takes for just + RT tasks (as the current "wakeup" does). This is useful + for those interested in wake up timings of RT tasks. + + "wakeup_dl" + + Traces and records the max latency that it takes for + a SCHED_DEADLINE task to be woken (as the "wakeup" and + "wakeup_rt" does). + + "mmiotrace" + + A special tracer that is used to trace binary module. + It will trace all the calls that a module makes to the + hardware. Everything it writes and reads from the I/O + as well. + + "branch" + + This tracer can be configured when tracing likely/unlikely + calls within the kernel. It will trace when a likely and + unlikely branch is hit and if it was correct in its prediction + of being correct. + + "nop" + + This is the "trace nothing" tracer. To remove all + tracers from tracing simply echo "nop" into + current_tracer. + + +Examples of using the tracer +---------------------------- + +Here are typical examples of using the tracers when controlling +them only with the tracefs interface (without using any +user-land utilities). + +Output format: +-------------- + +Here is an example of the output format of the file "trace":: + + # tracer: function + # + # entries-in-buffer/entries-written: 140080/250280 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath + bash-1977 [000] .... 17284.993653: __close_fd <-sys_close + bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd + sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify + bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock + bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd + bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock + bash-1977 [000] .... 17284.993657: filp_close <-__close_fd + bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close + sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath + .... + +A header is printed with the tracer name that is represented by +the trace. In this case the tracer is "function". Then it shows the +number of events in the buffer as well as the total number of entries +that were written. The difference is the number of entries that were +lost due to the buffer filling up (250280 - 140080 = 110200 events +lost). + +The header explains the content of the events. Task name "bash", the task +PID "1977", the CPU that it was running on "000", the latency format +(explained below), the timestamp in <secs>.<usecs> format, the +function name that was traced "sys_close" and the parent function that +called this function "system_call_fastpath". The timestamp is the time +at which the function was entered. + +Latency trace format +-------------------- + +When the latency-format option is enabled or when one of the latency +tracers is set, the trace file gives somewhat more information to see +why a latency happened. Here is a typical trace:: + + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: __lock_task_sighand + # => ended at: _raw_spin_unlock_irqrestore + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand + ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore + ps-6143 2d..1 306us : <stack trace> + => trace_hardirqs_on_caller + => trace_hardirqs_on + => _raw_spin_unlock_irqrestore + => do_task_stat + => proc_tgid_stat + => proc_single_show + => seq_read + => vfs_read + => sys_read + => system_call_fastpath + + +This shows that the current tracer is "irqsoff" tracing the time +for which interrupts were disabled. It gives the trace version (which +never changes) and the version of the kernel upon which this was executed on +(3.8). Then it displays the max latency in microseconds (259 us). The number +of trace entries displayed and the total number (both are four: #4/4). +VP, KP, SP, and HP are always zero and are reserved for later use. +#P is the number of online CPUs (#P:4). + +The task is the process that was running when the latency +occurred. (ps pid: 6143). + +The start and stop (the functions in which the interrupts were +disabled and enabled respectively) that caused the latencies: + + - __lock_task_sighand is where the interrupts were disabled. + - _raw_spin_unlock_irqrestore is where they were enabled again. + +The next lines after the header are the trace itself. The header +explains which is which. + + cmd: The name of the process in the trace. + + pid: The PID of that process. + + CPU#: The CPU which the process was running on. + + irqs-off: 'd' interrupts are disabled. '.' otherwise. + .. caution:: If the architecture does not support a way to + read the irq flags variable, an 'X' will always + be printed here. + + need-resched: + - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, + - 'n' only TIF_NEED_RESCHED is set, + - 'p' only PREEMPT_NEED_RESCHED is set, + - '.' otherwise. + + hardirq/softirq: + - 'Z' - NMI occurred inside a hardirq + - 'z' - NMI is running + - 'H' - hard irq occurred inside a softirq. + - 'h' - hard irq is running + - 's' - soft irq is running + - '.' - normal context. + + preempt-depth: The level of preempt_disabled + +The above is mostly meaningful for kernel developers. + + time: + When the latency-format option is enabled, the trace file + output includes a timestamp relative to the start of the + trace. This differs from the output when latency-format + is disabled, which includes an absolute timestamp. + + delay: + This is just to help catch your eye a bit better. And + needs to be fixed to be only relative to the same CPU. + The marks are determined by the difference between this + current trace and the next trace. + + - '$' - greater than 1 second + - '@' - greater than 100 milisecond + - '*' - greater than 10 milisecond + - '#' - greater than 1000 microsecond + - '!' - greater than 100 microsecond + - '+' - greater than 10 microsecond + - ' ' - less than or equal to 10 microsecond. + + The rest is the same as the 'trace' file. + + Note, the latency tracers will usually end with a back trace + to easily find where the latency occurred. + +trace_options +------------- + +The trace_options file (or the options directory) is used to control +what gets printed in the trace output, or manipulate the tracers. +To see what is available, simply cat the file:: + + cat trace_options + print-parent + nosym-offset + nosym-addr + noverbose + noraw + nohex + nobin + noblock + trace_printk + annotate + nouserstacktrace + nosym-userobj + noprintk-msg-only + context-info + nolatency-format + record-cmd + norecord-tgid + overwrite + nodisable_on_free + irq-info + markers + noevent-fork + function-trace + nofunction-fork + nodisplay-graph + nostacktrace + nobranch + +To disable one of the options, echo in the option prepended with +"no":: + + echo noprint-parent > trace_options + +To enable an option, leave off the "no":: + + echo sym-offset > trace_options + +Here are the available options: + + print-parent + On function traces, display the calling (parent) + function as well as the function being traced. + :: + + print-parent: + bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul + + noprint-parent: + bash-4000 [01] 1477.606694: simple_strtoul + + + sym-offset + Display not only the function name, but also the + offset in the function. For example, instead of + seeing just "ktime_get", you will see + "ktime_get+0xb/0x20". + :: + + sym-offset: + bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 + + sym-addr + This will also display the function address as well + as the function name. + :: + + sym-addr: + bash-4000 [01] 1477.606694: simple_strtoul <c0339346> + + verbose + This deals with the trace file when the + latency-format option is enabled. + :: + + bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ + (+0.000ms): simple_strtoul (kstrtoul) + + raw + This will display raw numbers. This option is best for + use with user applications that can translate the raw + numbers better than having it done in the kernel. + + hex + Similar to raw, but the numbers will be in a hexadecimal format. + + bin + This will print out the formats in raw binary. + + block + When set, reading trace_pipe will not block when polled. + + trace_printk + Can disable trace_printk() from writing into the buffer. + + annotate + It is sometimes confusing when the CPU buffers are full + and one CPU buffer had a lot of events recently, thus + a shorter time frame, were another CPU may have only had + a few events, which lets it have older events. When + the trace is reported, it shows the oldest events first, + and it may look like only one CPU ran (the one with the + oldest events). When the annotate option is set, it will + display when a new CPU buffer started:: + + <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on + <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on + <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore + ##### CPU 2 buffer started #### + <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle + <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog + <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock + + userstacktrace + This option changes the trace. It records a + stacktrace of the current user space thread after + each trace event. + + sym-userobj + when user stacktrace are enabled, look up which + object the address belongs to, and print a + relative address. This is especially useful when + ASLR is on, otherwise you don't get a chance to + resolve the address to object/file/line after + the app is no longer running + + The lookup is performed when you read + trace,trace_pipe. Example:: + + a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 + x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] + + + printk-msg-only + When set, trace_printk()s will only show the format + and not their parameters (if trace_bprintk() or + trace_bputs() was used to save the trace_printk()). + + context-info + Show only the event data. Hides the comm, PID, + timestamp, CPU, and other useful data. + + latency-format + This option changes the trace output. When it is enabled, + the trace displays additional information about the + latency, as described in "Latency trace format". + + record-cmd + When any event or tracer is enabled, a hook is enabled + in the sched_switch trace point to fill comm cache + with mapped pids and comms. But this may cause some + overhead, and if you only care about pids, and not the + name of the task, disabling this option can lower the + impact of tracing. See "saved_cmdlines". + + record-tgid + When any event or tracer is enabled, a hook is enabled + in the sched_switch trace point to fill the cache of + mapped Thread Group IDs (TGID) mapping to pids. See + "saved_tgids". + + overwrite + This controls what happens when the trace buffer is + full. If "1" (default), the oldest events are + discarded and overwritten. If "0", then the newest + events are discarded. + (see per_cpu/cpu0/stats for overrun and dropped) + + disable_on_free + When the free_buffer is closed, tracing will + stop (tracing_on set to 0). + + irq-info + Shows the interrupt, preempt count, need resched data. + When disabled, the trace looks like:: + + # tracer: function + # + # entries-in-buffer/entries-written: 144405/9452052 #P:4 + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up + <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 + <idle>-0 [002] 23636.756055: enqueue_task <-activate_task + + + markers + When set, the trace_marker is writable (only by root). + When disabled, the trace_marker will error with EINVAL + on write. + + event-fork + When set, tasks with PIDs listed in set_event_pid will have + the PIDs of their children added to set_event_pid when those + tasks fork. Also, when tasks with PIDs in set_event_pid exit, + their PIDs will be removed from the file. + + function-trace + The latency tracers will enable function tracing + if this option is enabled (default it is). When + it is disabled, the latency tracers do not trace + functions. This keeps the overhead of the tracer down + when performing latency tests. + + function-fork + When set, tasks with PIDs listed in set_ftrace_pid will + have the PIDs of their children added to set_ftrace_pid + when those tasks fork. Also, when tasks with PIDs in + set_ftrace_pid exit, their PIDs will be removed from the + file. + + display-graph + When set, the latency tracers (irqsoff, wakeup, etc) will + use function graph tracing instead of function tracing. + + stacktrace + When set, a stack trace is recorded after any trace event + is recorded. + + branch + Enable branch tracing with the tracer. This enables branch + tracer along with the currently set tracer. Enabling this + with the "nop" tracer is the same as just enabling the + "branch" tracer. + +.. tip:: Some tracers have their own options. They only appear in this + file when the tracer is active. They always appear in the + options directory. + + +Here are the per tracer options: + +Options for function tracer: + + func_stack_trace + When set, a stack trace is recorded after every + function that is recorded. NOTE! Limit the functions + that are recorded before enabling this, with + "set_ftrace_filter" otherwise the system performance + will be critically degraded. Remember to disable + this option before clearing the function filter. + +Options for function_graph tracer: + + Since the function_graph tracer has a slightly different output + it has its own options to control what is displayed. + + funcgraph-overrun + When set, the "overrun" of the graph stack is + displayed after each function traced. The + overrun, is when the stack depth of the calls + is greater than what is reserved for each task. + Each task has a fixed array of functions to + trace in the call graph. If the depth of the + calls exceeds that, the function is not traced. + The overrun is the number of functions missed + due to exceeding this array. + + funcgraph-cpu + When set, the CPU number of the CPU where the trace + occurred is displayed. + + funcgraph-overhead + When set, if the function takes longer than + A certain amount, then a delay marker is + displayed. See "delay" above, under the + header description. + + funcgraph-proc + Unlike other tracers, the process' command line + is not displayed by default, but instead only + when a task is traced in and out during a context + switch. Enabling this options has the command + of each process displayed at every line. + + funcgraph-duration + At the end of each function (the return) + the duration of the amount of time in the + function is displayed in microseconds. + + funcgraph-abstime + When set, the timestamp is displayed at each line. + + funcgraph-irqs + When disabled, functions that happen inside an + interrupt will not be traced. + + funcgraph-tail + When set, the return event will include the function + that it represents. By default this is off, and + only a closing curly bracket "}" is displayed for + the return of a function. + + sleep-time + When running function graph tracer, to include + the time a task schedules out in its function. + When enabled, it will account time the task has been + scheduled out as part of the function call. + + graph-time + When running function profiler with function graph tracer, + to include the time to call nested functions. When this is + not set, the time reported for the function will only + include the time the function itself executed for, not the + time for functions that it called. + +Options for blk tracer: + + blk_classic + Shows a more minimalistic output. + + +irqsoff +------- + +When interrupts are disabled, the CPU can not react to any other +external event (besides NMIs and SMIs). This prevents the timer +interrupt from triggering or the mouse interrupt from letting +the kernel know of a new mouse event. The result is a latency +with the reaction time. + +The irqsoff tracer tracks the time for which interrupts are +disabled. When a new maximum latency is hit, the tracer saves +the trace leading up to that latency point so that every time a +new maximum is reached, the old saved trace is discarded and the +new trace is saved. + +To reset the maximum, echo 0 into tracing_max_latency. Here is +an example:: + + # echo 0 > options/function-trace + # echo irqsoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: run_timer_softirq + # => ended at: run_timer_softirq + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq + <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq + <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq + <idle>-0 0dNs3 25us : <stack trace> + => _raw_spin_unlock_irq + => run_timer_softirq + => __do_softirq + => call_softirq + => do_softirq + => irq_exit + => smp_apic_timer_interrupt + => apic_timer_interrupt + => rcu_idle_exit + => cpu_idle + => rest_init + => start_kernel + => x86_64_start_reservations + => x86_64_start_kernel + +Here we see that that we had a latency of 16 microseconds (which is +very good). The _raw_spin_lock_irq in run_timer_softirq disabled +interrupts. The difference between the 16 and the displayed +timestamp 25us occurred because the clock was incremented +between the time of recording the max latency and the time of +recording the function that had that latency. + +Note the above example had function-trace not set. If we set +function-trace, we get a much larger output:: + + with echo 1 > options/function-trace + + # tracer: irqsoff + # + # irqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: ata_scsi_queuecmd + # => ended at: ata_scsi_queuecmd + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd + bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave + bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd + bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev + bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev + bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd + bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd + bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd + bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat + [...] + bash-2042 3d..1 67us : delay_tsc <-__delay + bash-2042 3d..1 67us : add_preempt_count <-delay_tsc + bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc + bash-2042 3d..1 67us : add_preempt_count <-delay_tsc + bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc + bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue + bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd + bash-2042 3d..1 120us : <stack trace> + => _raw_spin_unlock_irqrestore + => ata_scsi_queuecmd + => scsi_dispatch_cmd + => scsi_request_fn + => __blk_run_queue_uncond + => __blk_run_queue + => blk_queue_bio + => generic_make_request + => submit_bio + => submit_bh + => __ext3_get_inode_loc + => ext3_iget + => ext3_lookup + => lookup_real + => __lookup_hash + => walk_component + => lookup_last + => path_lookupat + => filename_lookup + => user_path_at_empty + => user_path_at + => vfs_fstatat + => vfs_stat + => sys_newstat + => system_call_fastpath + + +Here we traced a 71 microsecond latency. But we also see all the +functions that were called during that time. Note that by +enabling function tracing, we incur an added overhead. This +overhead may extend the latency times. But nevertheless, this +trace has provided some very helpful debugging information. + + +preemptoff +---------- + +When preemption is disabled, we may be able to receive +interrupts but the task cannot be preempted and a higher +priority task must wait for preemption to be enabled again +before it can preempt a lower priority task. + +The preemptoff tracer traces the places that disable preemption. +Like the irqsoff tracer, it records the maximum latency for +which preemption was disabled. The control of preemptoff tracer +is much like the irqsoff tracer. +:: + + # echo 0 > options/function-trace + # echo preemptoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: preemptoff + # + # preemptoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: do_IRQ + # => ended at: do_IRQ + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ + sshd-1991 1d..1 46us : irq_exit <-do_IRQ + sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ + sshd-1991 1d..1 52us : <stack trace> + => sub_preempt_count + => irq_exit + => do_IRQ + => ret_from_intr + + +This has some more changes. Preemption was disabled when an +interrupt came in (notice the 'h'), and was enabled on exit. +But we also see that interrupts have been disabled when entering +the preempt off section and leaving it (the 'd'). We do not know if +interrupts were enabled in the mean time or shortly after this +was over. +:: + + # tracer: preemptoff + # + # preemptoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: wake_up_new_task + # => ended at: task_rq_unlock + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task + bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq + bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair + bash-1994 1d..1 1us : source_load <-select_task_rq_fair + bash-1994 1d..1 1us : source_load <-select_task_rq_fair + [...] + bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt + bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter + bash-1994 1d..1 13us : add_preempt_count <-irq_enter + bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt + bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt + bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt + bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock + bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt + [...] + bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event + bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt + bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit + bash-1994 1d..2 36us : do_softirq <-irq_exit + bash-1994 1d..2 36us : __do_softirq <-call_softirq + bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq + bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq + bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq + bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock + bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq + [...] + bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks + bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq + bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable + bash-1994 1dN.2 82us : idle_cpu <-irq_exit + bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit + bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit + bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock + bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock + bash-1994 1.N.1 104us : <stack trace> + => sub_preempt_count + => _raw_spin_unlock_irqrestore + => task_rq_unlock + => wake_up_new_task + => do_fork + => sys_clone + => stub_clone + + +The above is an example of the preemptoff trace with +function-trace set. Here we see that interrupts were not disabled +the entire time. The irq_enter code lets us know that we entered +an interrupt 'h'. Before that, the functions being traced still +show that it is not in an interrupt, but we can see from the +functions themselves that this is not the case. + +preemptirqsoff +-------------- + +Knowing the locations that have interrupts disabled or +preemption disabled for the longest times is helpful. But +sometimes we would like to know when either preemption and/or +interrupts are disabled. + +Consider the following code:: + + local_irq_disable(); + call_function_with_irqs_off(); + preempt_disable(); + call_function_with_irqs_and_preemption_off(); + local_irq_enable(); + call_function_with_preemption_off(); + preempt_enable(); + +The irqsoff tracer will record the total length of +call_function_with_irqs_off() and +call_function_with_irqs_and_preemption_off(). + +The preemptoff tracer will record the total length of +call_function_with_irqs_and_preemption_off() and +call_function_with_preemption_off(). + +But neither will trace the time that interrupts and/or +preemption is disabled. This total time is the time that we can +not schedule. To record this time, use the preemptirqsoff +tracer. + +Again, using this trace is much like the irqsoff and preemptoff +tracers. +:: + + # echo 0 > options/function-trace + # echo preemptirqsoff > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # ls -ltr + [...] + # echo 0 > tracing_on + # cat trace + # tracer: preemptirqsoff + # + # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: ata_scsi_queuecmd + # => ended at: ata_scsi_queuecmd + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd + ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd + ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd + ls-2230 3...1 111us : <stack trace> + => sub_preempt_count + => _raw_spin_unlock_irqrestore + => ata_scsi_queuecmd + => scsi_dispatch_cmd + => scsi_request_fn + => __blk_run_queue_uncond + => __blk_run_queue + => blk_queue_bio + => generic_make_request + => submit_bio + => submit_bh + => ext3_bread + => ext3_dir_bread + => htree_dirblock_to_tree + => ext3_htree_fill_tree + => ext3_readdir + => vfs_readdir + => sys_getdents + => system_call_fastpath + + +The trace_hardirqs_off_thunk is called from assembly on x86 when +interrupts are disabled in the assembly code. Without the +function tracing, we do not know if interrupts were enabled +within the preemption points. We do see that it started with +preemption enabled. + +Here is a trace with function-trace set:: + + # tracer: preemptirqsoff + # + # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0) + # ----------------- + # => started at: schedule + # => ended at: mutex_unlock + # + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + kworker/-59 3...1 0us : __schedule <-schedule + kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch + kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq + kworker/-59 3d..2 1us : deactivate_task <-__schedule + kworker/-59 3d..2 1us : dequeue_task <-deactivate_task + kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task + kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task + kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair + kworker/-59 3d..2 2us : update_min_vruntime <-update_curr + kworker/-59 3d..2 3us : cpuacct_charge <-update_curr + kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge + kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge + kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair + kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair + kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair + kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair + kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair + kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair + kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule + kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping + kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule + kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task + kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair + kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair + kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity + ls-2269 3d..2 7us : finish_task_switch <-__schedule + ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch + ls-2269 3d..2 8us : do_IRQ <-ret_from_intr + ls-2269 3d..2 8us : irq_enter <-do_IRQ + ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter + ls-2269 3d..2 9us : add_preempt_count <-irq_enter + ls-2269 3d.h2 9us : exit_idle <-do_IRQ + [...] + ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock + ls-2269 3d.h2 20us : irq_exit <-do_IRQ + ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit + ls-2269 3d..3 21us : do_softirq <-irq_exit + ls-2269 3d..3 21us : __do_softirq <-call_softirq + ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq + ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip + ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip + ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr + ls-2269 3d.s5 31us : irq_enter <-do_IRQ + ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter + [...] + ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter + ls-2269 3d.s5 32us : add_preempt_count <-irq_enter + ls-2269 3d.H5 32us : exit_idle <-do_IRQ + ls-2269 3d.H5 32us : handle_irq <-do_IRQ + ls-2269 3d.H5 32us : irq_to_desc <-handle_irq + ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq + [...] + ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll + ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action + ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq + ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable + ls-2269 3d..3 159us : idle_cpu <-irq_exit + ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit + ls-2269 3d..3 160us : sub_preempt_count <-irq_exit + ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock + ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock + ls-2269 3d... 186us : <stack trace> + => __mutex_unlock_slowpath + => mutex_unlock + => process_output + => n_tty_write + => tty_write + => vfs_write + => sys_write + => system_call_fastpath + +This is an interesting trace. It started with kworker running and +scheduling out and ls taking over. But as soon as ls released the +rq lock and enabled interrupts (but not preemption) an interrupt +triggered. When the interrupt finished, it started running softirqs. +But while the softirq was running, another interrupt triggered. +When an interrupt is running inside a softirq, the annotation is 'H'. + + +wakeup +------ + +One common case that people are interested in tracing is the +time it takes for a task that is woken to actually wake up. +Now for non Real-Time tasks, this can be arbitrary. But tracing +it none the less can be interesting. + +Without function tracing:: + + # echo 0 > options/function-trace + # echo wakeup > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup + # + # wakeup latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H + <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d..3 15us : __schedule <-schedule + <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H + +The tracer only traces the highest priority task in the system +to avoid tracing the normal circumstances. Here we see that +the kworker with a nice priority of -20 (not very nice), took +just 15 microseconds from the time it woke up, to the time it +ran. + +Non Real-Time tasks are not that interesting. A more interesting +trace is to concentrate only on Real-Time tasks. + +wakeup_rt +--------- + +In a Real-Time environment it is very important to know the +wakeup time it takes for the highest priority task that is woken +up to the time that it executes. This is also known as "schedule +latency". I stress the point that this is about RT tasks. It is +also important to know the scheduling latency of non-RT tasks, +but the average schedule latency is better for non-RT tasks. +Tools like LatencyTop are more appropriate for such +measurements. + +Real-Time environments are interested in the worst case latency. +That is the longest latency it takes for something to happen, +and not the average. We can have a very fast scheduler that may +only have a large latency once in a while, but that would not +work well with Real-Time tasks. The wakeup_rt tracer was designed +to record the worst case wakeups of RT tasks. Non-RT tasks are +not recorded because the tracer only records one worst case and +tracing non-RT tasks that are unpredictable will overwrite the +worst case latency of RT tasks (just run the normal wakeup +tracer for a while to see that effect). + +Since this tracer only deals with RT tasks, we will run this +slightly differently than we did with the previous tracers. +Instead of performing an 'ls', we will run 'sleep 1' under +'chrt' which changes the priority of the task. +:: + + # echo 0 > options/function-trace + # echo wakeup_rt > current_tracer + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup + # + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep + <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d..3 5us : __schedule <-schedule + <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep + + +Running this on an idle system, we see that it only took 5 microseconds +to perform the task switch. Note, since the trace point in the schedule +is before the actual "switch", we stop the tracing when the recorded task +is about to schedule in. This may change if we add a new marker at the +end of the scheduler. + +Notice that the recorded task is 'sleep' with the PID of 2389 +and it has an rt_prio of 5. This priority is user-space priority +and not the internal kernel priority. The policy is 1 for +SCHED_FIFO and 2 for SCHED_RR. + +Note, that the trace data shows the internal priority (99 - rtprio). +:: + + <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep + +The 0:120:R means idle was running with a nice priority of 0 (120 - 120) +and in the running state 'R'. The sleep task was scheduled in with +2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94) +and it too is in the running state. + +Doing the same with chrt -r 5 and function-trace set. +:: + + echo 1 > options/function-trace + + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep + <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup + <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr + <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup + <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up + <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up + <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up + <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer + <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock + <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt + <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt + <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event + <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event + <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event + <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt + <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit + <idle>-0 3dN.2 9us : idle_cpu <-irq_exit + <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit + <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit + <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit + <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle + <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit + <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle + <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit + <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit + <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit + <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz + <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock + <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz + <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update + <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz + <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock + <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel + <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel + <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 + <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave + <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16 + <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer + <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram + <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event + <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event + <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event + <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel + <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit + <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward + <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward + <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 + <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns + <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns + <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 + <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave + <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns + <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns + <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns + <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event + <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event + <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event + <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns + <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore + <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit + <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks + <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle + <idle>-0 3.N.. 25us : schedule <-cpu_idle + <idle>-0 3.N.. 25us : __schedule <-preempt_schedule + <idle>-0 3.N.. 26us : add_preempt_count <-__schedule + <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule + <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch + <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch + <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule + <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq + <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule + <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task + <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task + <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt + <idle>-0 3d..3 29us : __schedule <-preempt_schedule + <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep + +This isn't that big of a trace, even with function tracing enabled, +so I included the entire trace. + +The interrupt went off while when the system was idle. Somewhere +before task_woken_rt() was called, the NEED_RESCHED flag was set, +this is indicated by the first occurrence of the 'N' flag. + +Latency tracing and events +-------------------------- +As function tracing can induce a much larger latency, but without +seeing what happens within the latency it is hard to know what +caused it. There is a middle ground, and that is with enabling +events. +:: + + # echo 0 > options/function-trace + # echo wakeup_rt > current_tracer + # echo 1 > events/enable + # echo 1 > tracing_on + # echo 0 > tracing_max_latency + # chrt -f 5 sleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: wakeup_rt + # + # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ + # -------------------------------------------------------------------- + # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) + # ----------------- + # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5) + # ----------------- + # + # _------=> CPU# + # / _-----=> irqs-off + # | / _----=> need-resched + # || / _---=> hardirq/softirq + # ||| / _--=> preempt-depth + # |||| / delay + # cmd pid ||||| time | caller + # \ / ||||| \ | / + <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep + <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up + <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002 + <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8 + <idle>-0 2.N.2 2us : power_end: cpu_id=2 + <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2 + <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0 + <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000 + <idle>-0 2.N.2 5us : rcu_utilization: Start context switch + <idle>-0 2.N.2 5us : rcu_utilization: End context switch + <idle>-0 2d..3 6us : __schedule <-schedule + <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep + + +Hardware Latency Detector +------------------------- + +The hardware latency detector is executed by enabling the "hwlat" tracer. + +NOTE, this tracer will affect the performance of the system as it will +periodically make a CPU constantly busy with interrupts disabled. +:: + + # echo hwlat > current_tracer + # sleep 100 + # cat trace + # tracer: hwlat + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940 + <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365 + <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062 + <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633 + <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961 + <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1 + + +The above output is somewhat the same in the header. All events will have +interrupts disabled 'd'. Under the FUNCTION title there is: + + #1 + This is the count of events recorded that were greater than the + tracing_threshold (See below). + + inner/outer(us): 12/14 + + This shows two numbers as "inner latency" and "outer latency". The test + runs in a loop checking a timestamp twice. The latency detected within + the two timestamps is the "inner latency" and the latency detected + after the previous timestamp and the next timestamp in the loop is + the "outer latency". + + ts:1499801089.066141940 + + The absolute timestamp that the event happened. + + nmi-total:4 nmi-count:1 + + On architectures that support it, if an NMI comes in during the + test, the time spent in NMI is reported in "nmi-total" (in + microseconds). + + All architectures that have NMIs will show the "nmi-count" if an + NMI comes in during the test. + +hwlat files: + + tracing_threshold + This gets automatically set to "10" to represent 10 + microseconds. This is the threshold of latency that + needs to be detected before the trace will be recorded. + + Note, when hwlat tracer is finished (another tracer is + written into "current_tracer"), the original value for + tracing_threshold is placed back into this file. + + hwlat_detector/width + The length of time the test runs with interrupts disabled. + + hwlat_detector/window + The length of time of the window which the test + runs. That is, the test will run for "width" + microseconds per "window" microseconds + + tracing_cpumask + When the test is started. A kernel thread is created that + runs the test. This thread will alternate between CPUs + listed in the tracing_cpumask between each period + (one "window"). To limit the test to specific CPUs + set the mask in this file to only the CPUs that the test + should run on. + +function +-------- + +This tracer is the function tracer. Enabling the function tracer +can be done from the debug file system. Make sure the +ftrace_enabled is set; otherwise this tracer is a nop. +See the "ftrace_enabled" section below. +:: + + # sysctl kernel.ftrace_enabled=1 + # echo function > current_tracer + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 24799/24799 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write + bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock + bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify + bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify + bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify + bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock + bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock + bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify + [...] + + +Note: function tracer uses ring buffers to store the above +entries. The newest data may overwrite the oldest data. +Sometimes using echo to stop the trace is not sufficient because +the tracing could have overwritten the data that you wanted to +record. For this reason, it is sometimes better to disable +tracing directly from a program. This allows you to stop the +tracing at the point that you hit the part that you are +interested in. To disable the tracing directly from a C program, +something like following code snippet can be used:: + + int trace_fd; + [...] + int main(int argc, char *argv[]) { + [...] + trace_fd = open(tracing_file("tracing_on"), O_WRONLY); + [...] + if (condition_hit()) { + write(trace_fd, "0", 1); + } + [...] + } + + +Single thread tracing +--------------------- + +By writing into set_ftrace_pid you can trace a +single thread. For example:: + + # cat set_ftrace_pid + no pid + # echo 3111 > set_ftrace_pid + # cat set_ftrace_pid + 3111 + # echo function > current_tracer + # cat trace | head + # tracer: function + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return + yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range + yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel + yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel + yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll + yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll + # echo > set_ftrace_pid + # cat trace |head + # tracer: function + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + ##### CPU 3 buffer started #### + yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait + yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry + yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry + yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit + yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit + +If you want to trace a function when executing, you could use +something like this simple program. +:: + + #include <stdio.h> + #include <stdlib.h> + #include <sys/types.h> + #include <sys/stat.h> + #include <fcntl.h> + #include <unistd.h> + #include <string.h> + + #define _STR(x) #x + #define STR(x) _STR(x) + #define MAX_PATH 256 + + const char *find_tracefs(void) + { + static char tracefs[MAX_PATH+1]; + static int tracefs_found; + char type[100]; + FILE *fp; + + if (tracefs_found) + return tracefs; + + if ((fp = fopen("/proc/mounts","r")) == NULL) { + perror("/proc/mounts"); + return NULL; + } + + while (fscanf(fp, "%*s %" + STR(MAX_PATH) + "s %99s %*s %*d %*d\n", + tracefs, type) == 2) { + if (strcmp(type, "tracefs") == 0) + break; + } + fclose(fp); + + if (strcmp(type, "tracefs") != 0) { + fprintf(stderr, "tracefs not mounted"); + return NULL; + } + + strcat(tracefs, "/tracing/"); + tracefs_found = 1; + + return tracefs; + } + + const char *tracing_file(const char *file_name) + { + static char trace_file[MAX_PATH+1]; + snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name); + return trace_file; + } + + int main (int argc, char **argv) + { + if (argc < 1) + exit(-1); + + if (fork() > 0) { + int fd, ffd; + char line[64]; + int s; + + ffd = open(tracing_file("current_tracer"), O_WRONLY); + if (ffd < 0) + exit(-1); + write(ffd, "nop", 3); + + fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); + s = sprintf(line, "%d\n", getpid()); + write(fd, line, s); + + write(ffd, "function", 8); + + close(fd); + close(ffd); + + execvp(argv[1], argv+1); + } + + return 0; + } + +Or this simple script! +:: + + #!/bin/bash + + tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts` + echo nop > $tracefs/tracing/current_tracer + echo 0 > $tracefs/tracing/tracing_on + echo $$ > $tracefs/tracing/set_ftrace_pid + echo function > $tracefs/tracing/current_tracer + echo 1 > $tracefs/tracing/tracing_on + exec "$@" + + +function graph tracer +--------------------------- + +This tracer is similar to the function tracer except that it +probes a function on its entry and its exit. This is done by +using a dynamically allocated stack of return addresses in each +task_struct. On function entry the tracer overwrites the return +address of each function traced to set a custom probe. Thus the +original return address is stored on the stack of return address +in the task_struct. + +Probing on both ends of a function leads to special features +such as: + +- measure of a function's time execution +- having a reliable call stack to draw function calls graph + +This tracer is useful in several situations: + +- you want to find the reason of a strange kernel behavior and + need to see what happens in detail on any areas (or specific + ones). + +- you are experiencing weird latencies but it's difficult to + find its origin. + +- you want to find quickly which path is taken by a specific + function + +- you just want to peek inside a working kernel and want to see + what happens there. + +:: + + # tracer: function_graph + # + # CPU DURATION FUNCTION CALLS + # | | | | | | | + + 0) | sys_open() { + 0) | do_sys_open() { + 0) | getname() { + 0) | kmem_cache_alloc() { + 0) 1.382 us | __might_sleep(); + 0) 2.478 us | } + 0) | strncpy_from_user() { + 0) | might_fault() { + 0) 1.389 us | __might_sleep(); + 0) 2.553 us | } + 0) 3.807 us | } + 0) 7.876 us | } + 0) | alloc_fd() { + 0) 0.668 us | _spin_lock(); + 0) 0.570 us | expand_files(); + 0) 0.586 us | _spin_unlock(); + + +There are several columns that can be dynamically +enabled/disabled. You can use every combination of options you +want, depending on your needs. + +- The cpu number on which the function executed is default + enabled. It is sometimes better to only trace one cpu (see + tracing_cpu_mask file) or you might sometimes see unordered + function calls while cpu tracing switch. + + - hide: echo nofuncgraph-cpu > trace_options + - show: echo funcgraph-cpu > trace_options + +- The duration (function's time of execution) is displayed on + the closing bracket line of a function or on the same line + than the current function in case of a leaf one. It is default + enabled. + + - hide: echo nofuncgraph-duration > trace_options + - show: echo funcgraph-duration > trace_options + +- The overhead field precedes the duration field in case of + reached duration thresholds. + + - hide: echo nofuncgraph-overhead > trace_options + - show: echo funcgraph-overhead > trace_options + - depends on: funcgraph-duration + + ie:: + + 3) # 1837.709 us | } /* __switch_to */ + 3) | finish_task_switch() { + 3) 0.313 us | _raw_spin_unlock_irq(); + 3) 3.177 us | } + 3) # 1889.063 us | } /* __schedule */ + 3) ! 140.417 us | } /* __schedule */ + 3) # 2034.948 us | } /* schedule */ + 3) * 33998.59 us | } /* schedule_preempt_disabled */ + + [...] + + 1) 0.260 us | msecs_to_jiffies(); + 1) 0.313 us | __rcu_read_unlock(); + 1) + 61.770 us | } + 1) + 64.479 us | } + 1) 0.313 us | rcu_bh_qs(); + 1) 0.313 us | __local_bh_enable(); + 1) ! 217.240 us | } + 1) 0.365 us | idle_cpu(); + 1) | rcu_irq_exit() { + 1) 0.417 us | rcu_eqs_enter_common.isra.47(); + 1) 3.125 us | } + 1) ! 227.812 us | } + 1) ! 457.395 us | } + 1) @ 119760.2 us | } + + [...] + + 2) | handle_IPI() { + 1) 6.979 us | } + 2) 0.417 us | scheduler_ipi(); + 1) 9.791 us | } + 1) + 12.917 us | } + 2) 3.490 us | } + 1) + 15.729 us | } + 1) + 18.542 us | } + 2) $ 3594274 us | } + +Flags:: + + + means that the function exceeded 10 usecs. + ! means that the function exceeded 100 usecs. + # means that the function exceeded 1000 usecs. + * means that the function exceeded 10 msecs. + @ means that the function exceeded 100 msecs. + $ means that the function exceeded 1 sec. + + +- The task/pid field displays the thread cmdline and pid which + executed the function. It is default disabled. + + - hide: echo nofuncgraph-proc > trace_options + - show: echo funcgraph-proc > trace_options + + ie:: + + # tracer: function_graph + # + # CPU TASK/PID DURATION FUNCTION CALLS + # | | | | | | | | | + 0) sh-4802 | | d_free() { + 0) sh-4802 | | call_rcu() { + 0) sh-4802 | | __call_rcu() { + 0) sh-4802 | 0.616 us | rcu_process_gp_end(); + 0) sh-4802 | 0.586 us | check_for_new_grace_period(); + 0) sh-4802 | 2.899 us | } + 0) sh-4802 | 4.040 us | } + 0) sh-4802 | 5.151 us | } + 0) sh-4802 | + 49.370 us | } + + +- The absolute time field is an absolute timestamp given by the + system clock since it started. A snapshot of this time is + given on each entry/exit of functions + + - hide: echo nofuncgraph-abstime > trace_options + - show: echo funcgraph-abstime > trace_options + + ie:: + + # + # TIME CPU DURATION FUNCTION CALLS + # | | | | | | | | + 360.774522 | 1) 0.541 us | } + 360.774522 | 1) 4.663 us | } + 360.774523 | 1) 0.541 us | __wake_up_bit(); + 360.774524 | 1) 6.796 us | } + 360.774524 | 1) 7.952 us | } + 360.774525 | 1) 9.063 us | } + 360.774525 | 1) 0.615 us | journal_mark_dirty(); + 360.774527 | 1) 0.578 us | __brelse(); + 360.774528 | 1) | reiserfs_prepare_for_journal() { + 360.774528 | 1) | unlock_buffer() { + 360.774529 | 1) | wake_up_bit() { + 360.774529 | 1) | bit_waitqueue() { + 360.774530 | 1) 0.594 us | __phys_addr(); + + +The function name is always displayed after the closing bracket +for a function if the start of that function is not in the +trace buffer. + +Display of the function name after the closing bracket may be +enabled for functions whose start is in the trace buffer, +allowing easier searching with grep for function durations. +It is default disabled. + + - hide: echo nofuncgraph-tail > trace_options + - show: echo funcgraph-tail > trace_options + + Example with nofuncgraph-tail (default):: + + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } + 0) 2.861 us | } + + Example with funcgraph-tail:: + + 0) | putname() { + 0) | kmem_cache_free() { + 0) 0.518 us | __phys_addr(); + 0) 1.757 us | } /* kmem_cache_free() */ + 0) 2.861 us | } /* putname() */ + +You can put some comments on specific functions by using +trace_printk() For example, if you want to put a comment inside +the __might_sleep() function, you just have to include +<linux/ftrace.h> and call trace_printk() inside __might_sleep():: + + trace_printk("I'm a comment!\n") + +will produce:: + + 1) | __might_sleep() { + 1) | /* I'm a comment! */ + 1) 1.449 us | } + + +You might find other useful features for this tracer in the +following "dynamic ftrace" section such as tracing only specific +functions or tasks. + +dynamic ftrace +-------------- + +If CONFIG_DYNAMIC_FTRACE is set, the system will run with +virtually no overhead when function tracing is disabled. The way +this works is the mcount function call (placed at the start of +every kernel function, produced by the -pg switch in gcc), +starts of pointing to a simple return. (Enabling FTRACE will +include the -pg switch in the compiling of the kernel.) + +At compile time every C file object is run through the +recordmcount program (located in the scripts directory). This +program will parse the ELF headers in the C object to find all +the locations in the .text section that call mcount. Starting +with gcc verson 4.6, the -mfentry has been added for x86, which +calls "__fentry__" instead of "mcount". Which is called before +the creation of the stack frame. + +Note, not all sections are traced. They may be prevented by either +a notrace, or blocked another way and all inline functions are not +traced. Check the "available_filter_functions" file to see what functions +can be traced. + +A section called "__mcount_loc" is created that holds +references to all the mcount/fentry call sites in the .text section. +The recordmcount program re-links this section back into the +original object. The final linking stage of the kernel will add all these +references into a single table. + +On boot up, before SMP is initialized, the dynamic ftrace code +scans this table and updates all the locations into nops. It +also records the locations, which are added to the +available_filter_functions list. Modules are processed as they +are loaded and before they are executed. When a module is +unloaded, it also removes its functions from the ftrace function +list. This is automatic in the module unload code, and the +module author does not need to worry about it. + +When tracing is enabled, the process of modifying the function +tracepoints is dependent on architecture. The old method is to use +kstop_machine to prevent races with the CPUs executing code being +modified (which can cause the CPU to do undesirable things, especially +if the modified code crosses cache (or page) boundaries), and the nops are +patched back to calls. But this time, they do not call mcount +(which is just a function stub). They now call into the ftrace +infrastructure. + +The new method of modifying the function tracepoints is to place +a breakpoint at the location to be modified, sync all CPUs, modify +the rest of the instruction not covered by the breakpoint. Sync +all CPUs again, and then remove the breakpoint with the finished +version to the ftrace call site. + +Some archs do not even need to monkey around with the synchronization, +and can just slap the new code on top of the old without any +problems with other CPUs executing it at the same time. + +One special side-effect to the recording of the functions being +traced is that we can now selectively choose which functions we +wish to trace and which ones we want the mcount calls to remain +as nops. + +Two files are used, one for enabling and one for disabling the +tracing of specified functions. They are: + + set_ftrace_filter + +and + + set_ftrace_notrace + +A list of available functions that you can add to these files is +listed in: + + available_filter_functions + +:: + + # cat available_filter_functions + put_prev_task_idle + kmem_cache_create + pick_next_task_rt + get_online_cpus + pick_next_task_fair + mutex_lock + [...] + +If I am only interested in sys_nanosleep and hrtimer_interrupt:: + + # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter + # echo function > current_tracer + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 5/5 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath + <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt + usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt + <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt + <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt + +To see which functions are being traced, you can cat the file: +:: + + # cat set_ftrace_filter + hrtimer_interrupt + sys_nanosleep + + +Perhaps this is not enough. The filters also allow glob(7) matching. + + ``<match>*`` + will match functions that begin with <match> + ``*<match>`` + will match functions that end with <match> + ``*<match>*`` + will match functions that have <match> in it + ``<match1>*<match2>`` + will match functions that begin with <match1> and end with <match2> + +.. note:: + It is better to use quotes to enclose the wild cards, + otherwise the shell may expand the parameters into names + of files in the local directory. + +:: + + # echo 'hrtimer_*' > set_ftrace_filter + +Produces:: + + # tracer: function + # + # entries-in-buffer/entries-written: 897/897 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit + <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel + <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer + <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit + <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 + <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt + <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter + <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem + +Notice that we lost the sys_nanosleep. +:: + + # cat set_ftrace_filter + hrtimer_run_queues + hrtimer_run_pending + hrtimer_init + hrtimer_cancel + hrtimer_try_to_cancel + hrtimer_forward + hrtimer_start + hrtimer_reprogram + hrtimer_force_reprogram + hrtimer_get_next_event + hrtimer_interrupt + hrtimer_nanosleep + hrtimer_wakeup + hrtimer_get_remaining + hrtimer_get_res + hrtimer_init_sleeper + + +This is because the '>' and '>>' act just like they do in bash. +To rewrite the filters, use '>' +To append to the filters, use '>>' + +To clear out a filter so that all functions will be recorded +again:: + + # echo > set_ftrace_filter + # cat set_ftrace_filter + # + +Again, now we want to append. + +:: + + # echo sys_nanosleep > set_ftrace_filter + # cat set_ftrace_filter + sys_nanosleep + # echo 'hrtimer_*' >> set_ftrace_filter + # cat set_ftrace_filter + hrtimer_run_queues + hrtimer_run_pending + hrtimer_init + hrtimer_cancel + hrtimer_try_to_cancel + hrtimer_forward + hrtimer_start + hrtimer_reprogram + hrtimer_force_reprogram + hrtimer_get_next_event + hrtimer_interrupt + sys_nanosleep + hrtimer_nanosleep + hrtimer_wakeup + hrtimer_get_remaining + hrtimer_get_res + hrtimer_init_sleeper + + +The set_ftrace_notrace prevents those functions from being +traced. +:: + + # echo '*preempt*' '*lock*' > set_ftrace_notrace + +Produces:: + + # tracer: function + # + # entries-in-buffer/entries-written: 39608/39608 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open + bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last + bash-1994 [000] .... 4342.324897: ima_file_check <-do_last + bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check + bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement + bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action + bash-1994 [000] .... 4342.324899: do_truncate <-do_last + bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate + bash-1994 [000] .... 4342.324899: notify_change <-do_truncate + bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change + bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time + bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time + +We can see that there's no more lock or preempt tracing. + + +Dynamic ftrace with the function graph tracer +--------------------------------------------- + +Although what has been explained above concerns both the +function tracer and the function-graph-tracer, there are some +special features only available in the function-graph tracer. + +If you want to trace only one function and all of its children, +you just have to echo its name into set_graph_function:: + + echo __do_fault > set_graph_function + +will produce the following "expanded" trace of the __do_fault() +function:: + + 0) | __do_fault() { + 0) | filemap_fault() { + 0) | find_lock_page() { + 0) 0.804 us | find_get_page(); + 0) | __might_sleep() { + 0) 1.329 us | } + 0) 3.904 us | } + 0) 4.979 us | } + 0) 0.653 us | _spin_lock(); + 0) 0.578 us | page_add_file_rmap(); + 0) 0.525 us | native_set_pte_at(); + 0) 0.585 us | _spin_unlock(); + 0) | unlock_page() { + 0) 0.541 us | page_waitqueue(); + 0) 0.639 us | __wake_up_bit(); + 0) 2.786 us | } + 0) + 14.237 us | } + 0) | __do_fault() { + 0) | filemap_fault() { + 0) | find_lock_page() { + 0) 0.698 us | find_get_page(); + 0) | __might_sleep() { + 0) 1.412 us | } + 0) 3.950 us | } + 0) 5.098 us | } + 0) 0.631 us | _spin_lock(); + 0) 0.571 us | page_add_file_rmap(); + 0) 0.526 us | native_set_pte_at(); + 0) 0.586 us | _spin_unlock(); + 0) | unlock_page() { + 0) 0.533 us | page_waitqueue(); + 0) 0.638 us | __wake_up_bit(); + 0) 2.793 us | } + 0) + 14.012 us | } + +You can also expand several functions at once:: + + echo sys_open > set_graph_function + echo sys_close >> set_graph_function + +Now if you want to go back to trace all functions you can clear +this special filter via:: + + echo > set_graph_function + + +ftrace_enabled +-------------- + +Note, the proc sysctl ftrace_enable is a big on/off switch for the +function tracer. By default it is enabled (when function tracing is +enabled in the kernel). If it is disabled, all function tracing is +disabled. This includes not only the function tracers for ftrace, but +also for any other uses (perf, kprobes, stack tracing, profiling, etc). + +Please disable this with care. + +This can be disable (and enabled) with:: + + sysctl kernel.ftrace_enabled=0 + sysctl kernel.ftrace_enabled=1 + + or + + echo 0 > /proc/sys/kernel/ftrace_enabled + echo 1 > /proc/sys/kernel/ftrace_enabled + + +Filter commands +--------------- + +A few commands are supported by the set_ftrace_filter interface. +Trace commands have the following format:: + + <function>:<command>:<parameter> + +The following commands are supported: + +- mod: + This command enables function filtering per module. The + parameter defines the module. For example, if only the write* + functions in the ext3 module are desired, run: + + echo 'write*:mod:ext3' > set_ftrace_filter + + This command interacts with the filter in the same way as + filtering based on function names. Thus, adding more functions + in a different module is accomplished by appending (>>) to the + filter file. Remove specific module functions by prepending + '!':: + + echo '!writeback*:mod:ext3' >> set_ftrace_filter + + Mod command supports module globbing. Disable tracing for all + functions except a specific module:: + + echo '!*:mod:!ext3' >> set_ftrace_filter + + Disable tracing for all modules, but still trace kernel:: + + echo '!*:mod:*' >> set_ftrace_filter + + Enable filter only for kernel:: + + echo '*write*:mod:!*' >> set_ftrace_filter + + Enable filter for module globbing:: + + echo '*write*:mod:*snd*' >> set_ftrace_filter + +- traceon/traceoff: + These commands turn tracing on and off when the specified + functions are hit. The parameter determines how many times the + tracing system is turned on and off. If unspecified, there is + no limit. For example, to disable tracing when a schedule bug + is hit the first 5 times, run:: + + echo '__schedule_bug:traceoff:5' > set_ftrace_filter + + To always disable tracing when __schedule_bug is hit:: + + echo '__schedule_bug:traceoff' > set_ftrace_filter + + These commands are cumulative whether or not they are appended + to set_ftrace_filter. To remove a command, prepend it by '!' + and drop the parameter:: + + echo '!__schedule_bug:traceoff:0' > set_ftrace_filter + + The above removes the traceoff command for __schedule_bug + that have a counter. To remove commands without counters:: + + echo '!__schedule_bug:traceoff' > set_ftrace_filter + +- snapshot: + Will cause a snapshot to be triggered when the function is hit. + :: + + echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter + + To only snapshot once: + :: + + echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter + + To remove the above commands:: + + echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter + echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter + +- enable_event/disable_event: + These commands can enable or disable a trace event. Note, because + function tracing callbacks are very sensitive, when these commands + are registered, the trace point is activated, but disabled in + a "soft" mode. That is, the tracepoint will be called, but + just will not be traced. The event tracepoint stays in this mode + as long as there's a command that triggers it. + :: + + echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \ + set_ftrace_filter + + The format is:: + + <function>:enable_event:<system>:<event>[:count] + <function>:disable_event:<system>:<event>[:count] + + To remove the events commands:: + + echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \ + set_ftrace_filter + echo '!schedule:disable_event:sched:sched_switch' > \ + set_ftrace_filter + +- dump: + When the function is hit, it will dump the contents of the ftrace + ring buffer to the console. This is useful if you need to debug + something, and want to dump the trace when a certain function + is hit. Perhaps its a function that is called before a tripple + fault happens and does not allow you to get a regular dump. + +- cpudump: + When the function is hit, it will dump the contents of the ftrace + ring buffer for the current CPU to the console. Unlike the "dump" + command, it only prints out the contents of the ring buffer for the + CPU that executed the function that triggered the dump. + +trace_pipe +---------- + +The trace_pipe outputs the same content as the trace file, but +the effect on the tracing is different. Every read from +trace_pipe is consumed. This means that subsequent reads will be +different. The trace is live. +:: + + # echo function > current_tracer + # cat trace_pipe > /tmp/trace.out & + [1] 4153 + # echo 1 > tracing_on + # usleep 1 + # echo 0 > tracing_on + # cat trace + # tracer: function + # + # entries-in-buffer/entries-written: 0/0 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + + # + # cat /tmp/trace.out + bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write + bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock + bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify + bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify + bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify + bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock + bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock + bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify + bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath + + +Note, reading the trace_pipe file will block until more input is +added. + +trace entries +------------- + +Having too much or not enough data can be troublesome in +diagnosing an issue in the kernel. The file buffer_size_kb is +used to modify the size of the internal trace buffers. The +number listed is the number of entries that can be recorded per +CPU. To know the full size, multiply the number of possible CPUs +with the number of entries. +:: + + # cat buffer_size_kb + 1408 (units kilobytes) + +Or simply read buffer_total_size_kb +:: + + # cat buffer_total_size_kb + 5632 + +To modify the buffer, simple echo in a number (in 1024 byte segments). +:: + + # echo 10000 > buffer_size_kb + # cat buffer_size_kb + 10000 (units kilobytes) + +It will try to allocate as much as possible. If you allocate too +much, it can cause Out-Of-Memory to trigger. +:: + + # echo 1000000000000 > buffer_size_kb + -bash: echo: write error: Cannot allocate memory + # cat buffer_size_kb + 85 + +The per_cpu buffers can be changed individually as well: +:: + + # echo 10000 > per_cpu/cpu0/buffer_size_kb + # echo 100 > per_cpu/cpu1/buffer_size_kb + +When the per_cpu buffers are not the same, the buffer_size_kb +at the top level will just show an X +:: + + # cat buffer_size_kb + X + +This is where the buffer_total_size_kb is useful: +:: + + # cat buffer_total_size_kb + 12916 + +Writing to the top level buffer_size_kb will reset all the buffers +to be the same again. + +Snapshot +-------- +CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature +available to all non latency tracers. (Latency tracers which +record max latency, such as "irqsoff" or "wakeup", can't use +this feature, since those are already using the snapshot +mechanism internally.) + +Snapshot preserves a current trace buffer at a particular point +in time without stopping tracing. Ftrace swaps the current +buffer with a spare buffer, and tracing continues in the new +current (=previous spare) buffer. + +The following tracefs files in "tracing" are related to this +feature: + + snapshot: + + This is used to take a snapshot and to read the output + of the snapshot. Echo 1 into this file to allocate a + spare buffer and to take a snapshot (swap), then read + the snapshot from this file in the same format as + "trace" (described above in the section "The File + System"). Both reads snapshot and tracing are executable + in parallel. When the spare buffer is allocated, echoing + 0 frees it, and echoing else (positive) values clear the + snapshot contents. + More details are shown in the table below. + + +--------------+------------+------------+------------+ + |status\\input | 0 | 1 | else | + +==============+============+============+============+ + |not allocated |(do nothing)| alloc+swap |(do nothing)| + +--------------+------------+------------+------------+ + |allocated | free | swap | clear | + +--------------+------------+------------+------------+ + +Here is an example of using the snapshot feature. +:: + + # echo 1 > events/sched/enable + # echo 1 > snapshot + # cat snapshot + # tracer: nop + # + # entries-in-buffer/entries-written: 71/71 #P:8 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120 + sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120 + [...] + <idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120 + + # cat trace + # tracer: nop + # + # entries-in-buffer/entries-written: 77/77 #P:8 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + <idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120 + snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120 + [...] + + +If you try to use this snapshot feature when current tracer is +one of the latency tracers, you will get the following results. +:: + + # echo wakeup > current_tracer + # echo 1 > snapshot + bash: echo: write error: Device or resource busy + # cat snapshot + cat: snapshot: Device or resource busy + + +Instances +--------- +In the tracefs tracing directory is a directory called "instances". +This directory can have new directories created inside of it using +mkdir, and removing directories with rmdir. The directory created +with mkdir in this directory will already contain files and other +directories after it is created. +:: + + # mkdir instances/foo + # ls instances/foo + buffer_size_kb buffer_total_size_kb events free_buffer per_cpu + set_event snapshot trace trace_clock trace_marker trace_options + trace_pipe tracing_on + +As you can see, the new directory looks similar to the tracing directory +itself. In fact, it is very similar, except that the buffer and +events are agnostic from the main director, or from any other +instances that are created. + +The files in the new directory work just like the files with the +same name in the tracing directory except the buffer that is used +is a separate and new buffer. The files affect that buffer but do not +affect the main buffer with the exception of trace_options. Currently, +the trace_options affect all instances and the top level buffer +the same, but this may change in future releases. That is, options +may become specific to the instance they reside in. + +Notice that none of the function tracer files are there, nor is +current_tracer and available_tracers. This is because the buffers +can currently only have events enabled for them. +:: + + # mkdir instances/foo + # mkdir instances/bar + # mkdir instances/zoot + # echo 100000 > buffer_size_kb + # echo 1000 > instances/foo/buffer_size_kb + # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb + # echo function > current_trace + # echo 1 > instances/foo/events/sched/sched_wakeup/enable + # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable + # echo 1 > instances/foo/events/sched/sched_switch/enable + # echo 1 > instances/bar/events/irq/enable + # echo 1 > instances/zoot/events/syscalls/enable + # cat trace_pipe + CPU:2 [LOST 11745 EVENTS] + bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist + bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave + bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist + bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist + bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock + bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype + bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist + bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist + bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics + bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics + bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process + [...] + + # cat instances/foo/trace_pipe + bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 + bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 + <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003 + <idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120 + rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120 + bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 + bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 + bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120 + kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001 + kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120 + [...] + + # cat instances/bar/trace_pipe + migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX] + <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX] + bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER] + bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU] + bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER] + bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER] + bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU] + bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU] + sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4 + sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled + sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0 + sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled + [...] + + # cat instances/zoot/trace + # tracer: nop + # + # entries-in-buffer/entries-written: 18996/18996 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + bash-1998 [000] d... 140.733501: sys_write -> 0x2 + bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1) + bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1 + bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0) + bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1 + bash-1998 [000] d... 140.733510: sys_close(fd: a) + bash-1998 [000] d... 140.733510: sys_close -> 0x0 + bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8) + bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0 + bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8) + bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0 + +You can see that the trace of the top most trace buffer shows only +the function tracing. The foo instance displays wakeups and task +switches. + +To remove the instances, simply delete their directories: +:: + + # rmdir instances/foo + # rmdir instances/bar + # rmdir instances/zoot + +Note, if a process has a trace file open in one of the instance +directories, the rmdir will fail with EBUSY. + + +Stack trace +----------- +Since the kernel has a fixed sized stack, it is important not to +waste it in functions. A kernel developer must be conscience of +what they allocate on the stack. If they add too much, the system +can be in danger of a stack overflow, and corruption will occur, +usually leading to a system panic. + +There are some tools that check this, usually with interrupts +periodically checking usage. But if you can perform a check +at every function call that will become very useful. As ftrace provides +a function tracer, it makes it convenient to check the stack size +at every function call. This is enabled via the stack tracer. + +CONFIG_STACK_TRACER enables the ftrace stack tracing functionality. +To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled. +:: + + # echo 1 > /proc/sys/kernel/stack_tracer_enabled + +You can also enable it from the kernel command line to trace +the stack size of the kernel during boot up, by adding "stacktrace" +to the kernel command line parameter. + +After running it for a few minutes, the output looks like: +:: + + # cat stack_max_size + 2928 + + # cat stack_trace + Depth Size Location (18 entries) + ----- ---- -------- + 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac + 1) 2704 160 find_busiest_group+0x31/0x1f1 + 2) 2544 256 load_balance+0xd9/0x662 + 3) 2288 80 idle_balance+0xbb/0x130 + 4) 2208 128 __schedule+0x26e/0x5b9 + 5) 2080 16 schedule+0x64/0x66 + 6) 2064 128 schedule_timeout+0x34/0xe0 + 7) 1936 112 wait_for_common+0x97/0xf1 + 8) 1824 16 wait_for_completion+0x1d/0x1f + 9) 1808 128 flush_work+0xfe/0x119 + 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20 + 11) 1664 48 input_available_p+0x1d/0x5c + 12) 1616 48 n_tty_poll+0x6d/0x134 + 13) 1568 64 tty_poll+0x64/0x7f + 14) 1504 880 do_select+0x31e/0x511 + 15) 624 400 core_sys_select+0x177/0x216 + 16) 224 96 sys_select+0x91/0xb9 + 17) 128 128 system_call_fastpath+0x16/0x1b + +Note, if -mfentry is being used by gcc, functions get traced before +they set up the stack frame. This means that leaf level functions +are not tested by the stack tracer when -mfentry is used. + +Currently, -mfentry is used by gcc 4.6.0 and above on x86 only. + +More +---- +More details can be found in the source code, in the `kernel/trace/*.c` files. diff --git a/Documentation/trace/function-graph-fold.vim b/Documentation/trace/function-graph-fold.vim new file mode 100644 index 000000000..0544b504c --- /dev/null +++ b/Documentation/trace/function-graph-fold.vim @@ -0,0 +1,42 @@ +" Enable folding for ftrace function_graph traces. +" +" To use, :source this file while viewing a function_graph trace, or use vim's +" -S option to load from the command-line together with a trace. You can then +" use the usual vim fold commands, such as "za", to open and close nested +" functions. While closed, a fold will show the total time taken for a call, +" as would normally appear on the line with the closing brace. Folded +" functions will not include finish_task_switch(), so folding should remain +" relatively sane even through a context switch. +" +" Note that this will almost certainly only work well with a +" single-CPU trace (e.g. trace-cmd report --cpu 1). + +function! FunctionGraphFoldExpr(lnum) + let line = getline(a:lnum) + if line[-1:] == '{' + if line =~ 'finish_task_switch() {$' + return '>1' + endif + return 'a1' + elseif line[-1:] == '}' + return 's1' + else + return '=' + endif +endfunction + +function! FunctionGraphFoldText() + let s = split(getline(v:foldstart), '|', 1) + if getline(v:foldend+1) =~ 'finish_task_switch() {$' + let s[2] = ' task switch ' + else + let e = split(getline(v:foldend), '|', 1) + let s[2] = e[2] + endif + return join(s, '|') +endfunction + +setlocal foldexpr=FunctionGraphFoldExpr(v:lnum) +setlocal foldtext=FunctionGraphFoldText() +setlocal foldcolumn=12 +setlocal foldmethod=expr diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst new file mode 100644 index 000000000..c14dab13a --- /dev/null +++ b/Documentation/trace/histogram.rst @@ -0,0 +1,2545 @@ +================ +Event Histograms +================ + +Documentation written by Tom Zanussi + +1. Introduction +=============== + + Histogram triggers are special event triggers that can be used to + aggregate trace event data into histograms. For information on + trace events and event triggers, see Documentation/trace/events.rst. + + +2. Histogram Trigger Command +============================ + + A histogram trigger command is an event trigger command that + aggregates event hits into a hash table keyed on one or more trace + event format fields (or stacktrace) and a set of running totals + derived from one or more trace event format fields and/or event + counts (hitcount). + + The format of a hist trigger is as follows:: + + hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>] + [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue] + [:clear][:name=histname1] [if <filter>] + + When a matching event is hit, an entry is added to a hash table + using the key(s) and value(s) named. Keys and values correspond to + fields in the event's format description. Values must correspond to + numeric fields - on an event hit, the value(s) will be added to a + sum kept for that field. The special string 'hitcount' can be used + in place of an explicit value field - this is simply a count of + event hits. If 'values' isn't specified, an implicit 'hitcount' + value will be automatically created and used as the only value. + Keys can be any field, or the special string 'stacktrace', which + will use the event's kernel stacktrace as the key. The keywords + 'keys' or 'key' can be used to specify keys, and the keywords + 'values', 'vals', or 'val' can be used to specify values. Compound + keys consisting of up to two fields can be specified by the 'keys' + keyword. Hashing a compound key produces a unique entry in the + table for each unique combination of component keys, and can be + useful for providing more fine-grained summaries of event data. + Additionally, sort keys consisting of up to two fields can be + specified by the 'sort' keyword. If more than one field is + specified, the result will be a 'sort within a sort': the first key + is taken to be the primary sort key and the second the secondary + key. If a hist trigger is given a name using the 'name' parameter, + its histogram data will be shared with other triggers of the same + name, and trigger hits will update this common data. Only triggers + with 'compatible' fields can be combined in this way; triggers are + 'compatible' if the fields named in the trigger share the same + number and type of fields and those fields also have the same names. + Note that any two events always share the compatible 'hitcount' and + 'stacktrace' fields and can therefore be combined using those + fields, however pointless that may be. + + 'hist' triggers add a 'hist' file to each event's subdirectory. + Reading the 'hist' file for the event will dump the hash table in + its entirety to stdout. If there are multiple hist triggers + attached to an event, there will be a table for each trigger in the + output. The table displayed for a named trigger will be the same as + any other instance having the same name. Each printed hash table + entry is a simple list of the keys and values comprising the entry; + keys are printed first and are delineated by curly braces, and are + followed by the set of value fields for the entry. By default, + numeric fields are displayed as base-10 integers. This can be + modified by appending any of the following modifiers to the field + name: + + =========== ========================================== + .hex display a number as a hex value + .sym display an address as a symbol + .sym-offset display an address as a symbol and offset + .syscall display a syscall id as a system call name + .execname display a common_pid as a program name + .log2 display log2 value rather than raw number + .usecs display a common_timestamp in microseconds + =========== ========================================== + + Note that in general the semantics of a given field aren't + interpreted when applying a modifier to it, but there are some + restrictions to be aware of in this regard: + + - only the 'hex' modifier can be used for values (because values + are essentially sums, and the other modifiers don't make sense + in that context). + - the 'execname' modifier can only be used on a 'common_pid'. The + reason for this is that the execname is simply the 'comm' value + saved for the 'current' process when an event was triggered, + which is the same as the common_pid value saved by the event + tracing code. Trying to apply that comm value to other pid + values wouldn't be correct, and typically events that care save + pid-specific comm fields in the event itself. + + A typical usage scenario would be the following to enable a hist + trigger, read its current contents, and then turn it off:: + + # echo 'hist:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger + + # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist + + # echo '!hist:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger + + The trigger file itself can be read to show the details of the + currently attached hist trigger. This information is also displayed + at the top of the 'hist' file when read. + + By default, the size of the hash table is 2048 entries. The 'size' + parameter can be used to specify more or fewer than that. The units + are in terms of hashtable entries - if a run uses more entries than + specified, the results will show the number of 'drops', the number + of hits that were ignored. The size should be a power of 2 between + 128 and 131072 (any non- power-of-2 number specified will be rounded + up). + + The 'sort' parameter can be used to specify a value field to sort + on. The default if unspecified is 'hitcount' and the default sort + order is 'ascending'. To sort in the opposite direction, append + .descending' to the sort key. + + The 'pause' parameter can be used to pause an existing hist trigger + or to start a hist trigger but not log any events until told to do + so. 'continue' or 'cont' can be used to start or restart a paused + hist trigger. + + The 'clear' parameter will clear the contents of a running hist + trigger and leave its current paused/active state. + + Note that the 'pause', 'cont', and 'clear' parameters should be + applied using 'append' shell operator ('>>') if applied to an + existing trigger, rather than via the '>' operator, which will cause + the trigger to be removed through truncation. + +- enable_hist/disable_hist + + The enable_hist and disable_hist triggers can be used to have one + event conditionally start and stop another event's already-attached + hist trigger. Any number of enable_hist and disable_hist triggers + can be attached to a given event, allowing that event to kick off + and stop aggregations on a host of other events. + + The format is very similar to the enable/disable_event triggers:: + + enable_hist:<system>:<event>[:count] + disable_hist:<system>:<event>[:count] + + Instead of enabling or disabling the tracing of the target event + into the trace buffer as the enable/disable_event triggers do, the + enable/disable_hist triggers enable or disable the aggregation of + the target event into a hash table. + + A typical usage scenario for the enable_hist/disable_hist triggers + would be to first set up a paused hist trigger on some event, + followed by an enable_hist/disable_hist pair that turns the hist + aggregation on and off when conditions of interest are hit:: + + # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + + # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger + + # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger + + The above sets up an initially paused hist trigger which is unpaused + and starts aggregating events when a given program is executed, and + which stops aggregating when the process exits and the hist trigger + is paused again. + + The examples below provide a more concrete illustration of the + concepts and typical usage patterns discussed above. + +'special' event fields +------------------------ + + There are a number of 'special event fields' available for use as + keys or values in a hist trigger. These look like and behave as if + they were actual event fields, but aren't really part of the event's + field definition or format file. They are however available for any + event, and can be used anywhere an actual event field could be. + They are: + + ====================== ==== ======================================= + common_timestamp u64 timestamp (from ring buffer) associated + with the event, in nanoseconds. May be + modified by .usecs to have timestamps + interpreted as microseconds. + common_cpu int the cpu on which the event occurred. + ====================== ==== ======================================= + +Extended error information +-------------------------- + + For some error conditions encountered when invoking a hist trigger + command, extended error information is available via the + corresponding event's 'hist' file. Reading the hist file after an + error will display more detailed information about what went wrong, + if information is available. This extended error information will + be available until the next hist trigger command for that event. + + If available for a given error condition, the extended error + information and usage takes the following form:: + + # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger + echo: write error: Invalid argument + + # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist + ERROR: Couldn't yyy: zzz + Last command: xxx + +6.2 'hist' trigger examples +--------------------------- + + The first set of examples creates aggregations using the kmalloc + event. The fields that can be used for the hist trigger are listed + in the kmalloc event's format file:: + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format + name: kmalloc + ID: 374 + format: + field:unsigned short common_type; offset:0; size:2; signed:0; + field:unsigned char common_flags; offset:2; size:1; signed:0; + field:unsigned char common_preempt_count; offset:3; size:1; signed:0; + field:int common_pid; offset:4; size:4; signed:1; + + field:unsigned long call_site; offset:8; size:8; signed:0; + field:const void * ptr; offset:16; size:8; signed:0; + field:size_t bytes_req; offset:24; size:8; signed:0; + field:size_t bytes_alloc; offset:32; size:8; signed:0; + field:gfp_t gfp_flags; offset:40; size:4; signed:0; + + We'll start by creating a hist trigger that generates a simple table + that lists the total number of bytes requested for each function in + the kernel that made one or more calls to kmalloc:: + + # echo 'hist:key=call_site:val=bytes_req' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + This tells the tracing system to create a 'hist' trigger using the + call_site field of the kmalloc event as the key for the table, which + just means that each unique call_site address will have an entry + created for it in the table. The 'val=bytes_req' parameter tells + the hist trigger that for each unique entry (call_site) in the + table, it should keep a running total of the number of bytes + requested by that call_site. + + We'll let it run for awhile and then dump the contents of the 'hist' + file in the kmalloc event's subdirectory (for readability, a number + of entries have been omitted):: + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] + + { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176 + { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024 + { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384 + { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24 + { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8 + { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152 + { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144 + { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144 + { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560 + { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736 + . + . + . + { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576 + { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336 + { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504 + { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584 + { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448 + { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720 + { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088 + { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920 + { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716 + { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712 + { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160 + { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520 + + Totals: + Hits: 4610 + Entries: 45 + Dropped: 0 + + The output displays a line for each entry, beginning with the key + specified in the trigger, followed by the value(s) also specified in + the trigger. At the beginning of the output is a line that displays + the trigger info, which can also be displayed by reading the + 'trigger' file:: + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active] + + At the end of the output are a few lines that display the overall + totals for the run. The 'Hits' field shows the total number of + times the event trigger was hit, the 'Entries' field shows the total + number of used entries in the hash table, and the 'Dropped' field + shows the number of hits that were dropped because the number of + used entries for the run exceeded the maximum number of entries + allowed for the table (normally 0, but if not a hint that you may + want to increase the size of the table using the 'size' parameter). + + Notice in the above output that there's an extra field, 'hitcount', + which wasn't specified in the trigger. Also notice that in the + trigger info output, there's a parameter, 'sort=hitcount', which + wasn't specified in the trigger either. The reason for that is that + every trigger implicitly keeps a count of the total number of hits + attributed to a given entry, called the 'hitcount'. That hitcount + information is explicitly displayed in the output, and in the + absence of a user-specified sort parameter, is used as the default + sort field. + + The value 'hitcount' can be used in place of an explicit value in + the 'values' parameter if you don't really need to have any + particular field summed and are mainly interested in hit + frequencies. + + To turn the hist trigger off, simply call up the trigger in the + command history and re-execute it with a '!' prepended:: + + # echo '!hist:key=call_site:val=bytes_req' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + Finally, notice that the call_site as displayed in the output above + isn't really very useful. It's an address, but normally addresses + are displayed in hex. To have a numeric field displayed as a hex + value, simply append '.hex' to the field name in the trigger:: + + # echo 'hist:key=call_site.hex:val=bytes_req' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active] + + { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433 + { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176 + { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384 + { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8 + { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511 + { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12 + { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152 + { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24 + { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144 + { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648 + { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144 + { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544 + . + . + . + { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024 + { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680 + { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112 + { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232 + { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360 + { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640 + { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600 + { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584 + { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656 + { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456 + { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600 + + Totals: + Hits: 4775 + Entries: 46 + Dropped: 0 + + Even that's only marginally more useful - while hex values do look + more like addresses, what users are typically more interested in + when looking at text addresses are the corresponding symbols + instead. To have an address displayed as symbolic value instead, + simply append '.sym' or '.sym-offset' to the field name in the + trigger:: + + # echo 'hist:key=call_site.sym:val=bytes_req' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active] + + { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024 + { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 + { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 + { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192 + { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 + { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40 + { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 + { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528 + { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624 + { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96 + { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464 + { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304 + { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 + { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424 + . + . + . + { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240 + { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280 + { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672 + { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208 + { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840 + { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312 + { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152 + { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576 + { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248 + { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384 + { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584 + { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176 + { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265 + + Totals: + Hits: 109928 + Entries: 71 + Dropped: 0 + + Because the default sort key above is 'hitcount', the above shows a + the list of call_sites by increasing hitcount, so that at the bottom + we see the functions that made the most kmalloc calls during the + run. If instead we we wanted to see the top kmalloc callers in + terms of the number of bytes requested rather than the number of + calls, and we wanted the top caller to appear at the top, we can use + the 'sort' parameter, along with the 'descending' modifier:: + + # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active] + + { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464 + { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176 + { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135 + { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128 + { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784 + { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992 + { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072 + { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824 + { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704 + { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088 + { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536 + { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664 + { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632 + . + . + . + { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 + { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 + { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48 + { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48 + { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48 + { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40 + { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16 + { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 + { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 + { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 + + Totals: + Hits: 32133 + Entries: 81 + Dropped: 0 + + To display the offset and size information in addition to the symbol + name, just use 'sym-offset' instead:: + + # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active] + + { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720 + { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936 + { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936 + { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832 + { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384 + { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040 + { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072 + { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880 + { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488 + { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696 + { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640 + { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456 + . + . + . + { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128 + { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96 + { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96 + { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84 + { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8 + { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7 + { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7 + + Totals: + Hits: 26098 + Entries: 64 + Dropped: 0 + + We can also add multiple fields to the 'values' parameter. For + example, we might want to see the total number of bytes allocated + alongside bytes requested, and display the result sorted by bytes + allocated in a descending order:: + + # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active] + + { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016 + { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224 + { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568 + { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760 + { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744 + { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400 + { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496 + { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304 + { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640 + { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760 + { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312 + { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432 + . + . + . + { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192 + { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 + { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 + { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 + { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128 + { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96 + { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64 + { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8 + { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8 + { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8 + + Totals: + Hits: 66598 + Entries: 65 + Dropped: 0 + + Finally, to finish off our kmalloc example, instead of simply having + the hist trigger display symbolic call_sites, we can have the hist + trigger additionally display the complete set of kernel stack traces + that led to each call_site. To do that, we simply use the special + value 'stacktrace' for the key parameter:: + + # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \ + /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger + + The above trigger will use the kernel stack trace in effect when an + event is triggered as the key for the hash table. This allows the + enumeration of every kernel callpath that led up to a particular + event, along with a running total of any of the event fields for + that event. Here we tally bytes requested and bytes allocated for + every callpath in the system that led up to a kmalloc (in this case + every callpath to a kmalloc for a kernel compile):: + + # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist + # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active] + + { stacktrace: + __kmalloc_track_caller+0x10b/0x1a0 + kmemdup+0x20/0x50 + hidraw_report_event+0x8a/0x120 [hid] + hid_report_raw_event+0x3ea/0x440 [hid] + hid_input_report+0x112/0x190 [hid] + hid_irq_in+0xc2/0x260 [usbhid] + __usb_hcd_giveback_urb+0x72/0x120 + usb_giveback_urb_bh+0x9e/0xe0 + tasklet_hi_action+0xf8/0x100 + __do_softirq+0x114/0x2c0 + irq_exit+0xa5/0xb0 + do_IRQ+0x5a/0xf0 + ret_from_intr+0x0/0x30 + cpuidle_enter+0x17/0x20 + cpu_startup_entry+0x315/0x3e0 + rest_init+0x7c/0x80 + } hitcount: 3 bytes_req: 21 bytes_alloc: 24 + { stacktrace: + __kmalloc_track_caller+0x10b/0x1a0 + kmemdup+0x20/0x50 + hidraw_report_event+0x8a/0x120 [hid] + hid_report_raw_event+0x3ea/0x440 [hid] + hid_input_report+0x112/0x190 [hid] + hid_irq_in+0xc2/0x260 [usbhid] + __usb_hcd_giveback_urb+0x72/0x120 + usb_giveback_urb_bh+0x9e/0xe0 + tasklet_hi_action+0xf8/0x100 + __do_softirq+0x114/0x2c0 + irq_exit+0xa5/0xb0 + do_IRQ+0x5a/0xf0 + ret_from_intr+0x0/0x30 + } hitcount: 3 bytes_req: 21 bytes_alloc: 24 + { stacktrace: + kmem_cache_alloc_trace+0xeb/0x150 + aa_alloc_task_context+0x27/0x40 + apparmor_cred_prepare+0x1f/0x50 + security_prepare_creds+0x16/0x20 + prepare_creds+0xdf/0x1a0 + SyS_capset+0xb5/0x200 + system_call_fastpath+0x12/0x6a + } hitcount: 1 bytes_req: 32 bytes_alloc: 32 + . + . + . + { stacktrace: + __kmalloc+0x11b/0x1b0 + i915_gem_execbuffer2+0x6c/0x2c0 [i915] + drm_ioctl+0x349/0x670 [drm] + do_vfs_ioctl+0x2f0/0x4f0 + SyS_ioctl+0x81/0xa0 + system_call_fastpath+0x12/0x6a + } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808 + { stacktrace: + __kmalloc+0x11b/0x1b0 + load_elf_phdrs+0x76/0xa0 + load_elf_binary+0x102/0x1650 + search_binary_handler+0x97/0x1d0 + do_execveat_common.isra.34+0x551/0x6e0 + SyS_execve+0x3a/0x50 + return_from_execve+0x0/0x23 + } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048 + { stacktrace: + kmem_cache_alloc_trace+0xeb/0x150 + apparmor_file_alloc_security+0x27/0x40 + security_file_alloc+0x16/0x20 + get_empty_filp+0x93/0x1c0 + path_openat+0x31/0x5f0 + do_filp_open+0x3a/0x90 + do_sys_open+0x128/0x220 + SyS_open+0x1e/0x20 + system_call_fastpath+0x12/0x6a + } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376 + { stacktrace: + __kmalloc+0x11b/0x1b0 + seq_buf_alloc+0x1b/0x50 + seq_read+0x2cc/0x370 + proc_reg_read+0x3d/0x80 + __vfs_read+0x28/0xe0 + vfs_read+0x86/0x140 + SyS_read+0x46/0xb0 + system_call_fastpath+0x12/0x6a + } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768 + + Totals: + Hits: 6085872 + Entries: 253 + Dropped: 0 + + If you key a hist trigger on common_pid, in order for example to + gather and display sorted totals for each process, you can use the + special .execname modifier to display the executable names for the + processes in the table rather than raw pids. The example below + keeps a per-process sum of total bytes read:: + + # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger + + # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist + # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active] + + { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512 + { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640 + { common_pid: compiz [ 2889] } hitcount: 59 count: 254400 + { common_pid: bash [ 8710] } hitcount: 3 count: 66369 + { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739 + { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648 + { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216 + { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396 + { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264 + { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424 + { common_pid: gmain [ 1315] } hitcount: 18 count: 6336 + . + . + . + { common_pid: postgres [ 1892] } hitcount: 2 count: 32 + { common_pid: postgres [ 1891] } hitcount: 2 count: 32 + { common_pid: gmain [ 8704] } hitcount: 2 count: 32 + { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21 + { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16 + { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16 + { common_pid: gdbus [ 2998] } hitcount: 1 count: 16 + { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8 + { common_pid: init [ 1] } hitcount: 2 count: 2 + + Totals: + Hits: 2116 + Entries: 51 + Dropped: 0 + + Similarly, if you key a hist trigger on syscall id, for example to + gather and display a list of systemwide syscall hits, you can use + the special .syscall modifier to display the syscall names rather + than raw ids. The example below keeps a running total of syscall + counts for the system during the run:: + + # echo 'hist:key=id.syscall:val=hitcount' > \ + /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger + + # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist + # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active] + + { id: sys_fsync [ 74] } hitcount: 1 + { id: sys_newuname [ 63] } hitcount: 1 + { id: sys_prctl [157] } hitcount: 1 + { id: sys_statfs [137] } hitcount: 1 + { id: sys_symlink [ 88] } hitcount: 1 + { id: sys_sendmmsg [307] } hitcount: 1 + { id: sys_semctl [ 66] } hitcount: 1 + { id: sys_readlink [ 89] } hitcount: 3 + { id: sys_bind [ 49] } hitcount: 3 + { id: sys_getsockname [ 51] } hitcount: 3 + { id: sys_unlink [ 87] } hitcount: 3 + { id: sys_rename [ 82] } hitcount: 4 + { id: unknown_syscall [ 58] } hitcount: 4 + { id: sys_connect [ 42] } hitcount: 4 + { id: sys_getpid [ 39] } hitcount: 4 + . + . + . + { id: sys_rt_sigprocmask [ 14] } hitcount: 952 + { id: sys_futex [202] } hitcount: 1534 + { id: sys_write [ 1] } hitcount: 2689 + { id: sys_setitimer [ 38] } hitcount: 2797 + { id: sys_read [ 0] } hitcount: 3202 + { id: sys_select [ 23] } hitcount: 3773 + { id: sys_writev [ 20] } hitcount: 4531 + { id: sys_poll [ 7] } hitcount: 8314 + { id: sys_recvmsg [ 47] } hitcount: 13738 + { id: sys_ioctl [ 16] } hitcount: 21843 + + Totals: + Hits: 67612 + Entries: 72 + Dropped: 0 + + The syscall counts above provide a rough overall picture of system + call activity on the system; we can see for example that the most + popular system call on this system was the 'sys_ioctl' system call. + + We can use 'compound' keys to refine that number and provide some + further insight as to which processes exactly contribute to the + overall ioctl count. + + The command below keeps a hitcount for every unique combination of + system call id and pid - the end result is essentially a table + that keeps a per-pid sum of system call hits. The results are + sorted using the system call id as the primary key, and the + hitcount sum as the secondary key:: + + # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \ + /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger + + # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist + # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active] + + { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1 + { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1 + { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1 + { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1 + { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2 + { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2 + { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2 + { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2 + { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2 + { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2 + . + . + . + { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12 + { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16 + { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808 + { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580 + . + . + . + { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3 + { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4 + { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6 + { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2 + { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4 + { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6 + + Totals: + Hits: 31536 + Entries: 323 + Dropped: 0 + + The above list does give us a breakdown of the ioctl syscall by + pid, but it also gives us quite a bit more than that, which we + don't really care about at the moment. Since we know the syscall + id for sys_ioctl (16, displayed next to the sys_ioctl name), we + can use that to filter out all the other syscalls:: + + # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \ + /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger + + # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist + # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active] + + { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1 + { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1 + . + . + . + { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45 + { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48 + { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48 + { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66 + { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674 + { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443 + + Totals: + Hits: 101162 + Entries: 103 + Dropped: 0 + + The above output shows that 'compiz' and 'Xorg' are far and away + the heaviest ioctl callers (which might lead to questions about + whether they really need to be making all those calls and to + possible avenues for further investigation.) + + The compound key examples used a key and a sum value (hitcount) to + sort the output, but we can just as easily use two keys instead. + Here's an example where we use a compound key composed of the the + common_pid and size event fields. Sorting with pid as the primary + key and 'size' as the secondary key allows us to display an + ordered summary of the recvfrom sizes, with counts, received by + each process:: + + # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \ + /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger + + # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist + # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active] + + { common_pid: smbd [ 784], size: 4 } hitcount: 1 + { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672 + { common_pid: postgres [ 1796], size: 1000 } hitcount: 6 + { common_pid: postgres [ 1867], size: 1000 } hitcount: 10 + { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2 + { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1 + { common_pid: compiz [ 2994], size: 8 } hitcount: 1 + { common_pid: compiz [ 2994], size: 20 } hitcount: 11 + { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2 + { common_pid: firefox [ 8817], size: 4 } hitcount: 1 + { common_pid: firefox [ 8817], size: 8 } hitcount: 5 + { common_pid: firefox [ 8817], size: 588 } hitcount: 2 + { common_pid: firefox [ 8817], size: 628 } hitcount: 1 + { common_pid: firefox [ 8817], size: 6944 } hitcount: 1 + { common_pid: firefox [ 8817], size: 408880 } hitcount: 2 + { common_pid: firefox [ 8822], size: 8 } hitcount: 2 + { common_pid: firefox [ 8822], size: 160 } hitcount: 2 + { common_pid: firefox [ 8822], size: 320 } hitcount: 2 + { common_pid: firefox [ 8822], size: 352 } hitcount: 1 + . + . + . + { common_pid: pool [ 8923], size: 1960 } hitcount: 10 + { common_pid: pool [ 8923], size: 2048 } hitcount: 10 + { common_pid: pool [ 8924], size: 1960 } hitcount: 10 + { common_pid: pool [ 8924], size: 2048 } hitcount: 10 + { common_pid: pool [ 8928], size: 1964 } hitcount: 4 + { common_pid: pool [ 8928], size: 1965 } hitcount: 2 + { common_pid: pool [ 8928], size: 2048 } hitcount: 6 + { common_pid: pool [ 8929], size: 1982 } hitcount: 1 + { common_pid: pool [ 8929], size: 2048 } hitcount: 1 + + Totals: + Hits: 2016 + Entries: 224 + Dropped: 0 + + The above example also illustrates the fact that although a compound + key is treated as a single entity for hashing purposes, the sub-keys + it's composed of can be accessed independently. + + The next example uses a string field as the hash key and + demonstrates how you can manually pause and continue a hist trigger. + In this example, we'll aggregate fork counts and don't expect a + large number of entries in the hash table, so we'll drop it to a + much smaller number, say 256:: + + # echo 'hist:key=child_comm:val=hitcount:size=256' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist + # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active] + + { child_comm: dconf worker } hitcount: 1 + { child_comm: ibus-daemon } hitcount: 1 + { child_comm: whoopsie } hitcount: 1 + { child_comm: smbd } hitcount: 1 + { child_comm: gdbus } hitcount: 1 + { child_comm: kthreadd } hitcount: 1 + { child_comm: dconf worker } hitcount: 1 + { child_comm: evolution-alarm } hitcount: 2 + { child_comm: Socket Thread } hitcount: 2 + { child_comm: postgres } hitcount: 2 + { child_comm: bash } hitcount: 3 + { child_comm: compiz } hitcount: 3 + { child_comm: evolution-sourc } hitcount: 4 + { child_comm: dhclient } hitcount: 4 + { child_comm: pool } hitcount: 5 + { child_comm: nm-dispatcher.a } hitcount: 8 + { child_comm: firefox } hitcount: 8 + { child_comm: dbus-daemon } hitcount: 8 + { child_comm: glib-pacrunner } hitcount: 10 + { child_comm: evolution } hitcount: 23 + + Totals: + Hits: 89 + Entries: 20 + Dropped: 0 + + If we want to pause the hist trigger, we can simply append :pause to + the command that started the trigger. Notice that the trigger info + displays as [paused]:: + + # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \ + /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist + # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused] + + { child_comm: dconf worker } hitcount: 1 + { child_comm: kthreadd } hitcount: 1 + { child_comm: dconf worker } hitcount: 1 + { child_comm: gdbus } hitcount: 1 + { child_comm: ibus-daemon } hitcount: 1 + { child_comm: Socket Thread } hitcount: 2 + { child_comm: evolution-alarm } hitcount: 2 + { child_comm: smbd } hitcount: 2 + { child_comm: bash } hitcount: 3 + { child_comm: whoopsie } hitcount: 3 + { child_comm: compiz } hitcount: 3 + { child_comm: evolution-sourc } hitcount: 4 + { child_comm: pool } hitcount: 5 + { child_comm: postgres } hitcount: 6 + { child_comm: firefox } hitcount: 8 + { child_comm: dhclient } hitcount: 10 + { child_comm: emacs } hitcount: 12 + { child_comm: dbus-daemon } hitcount: 20 + { child_comm: nm-dispatcher.a } hitcount: 20 + { child_comm: evolution } hitcount: 35 + { child_comm: glib-pacrunner } hitcount: 59 + + Totals: + Hits: 199 + Entries: 21 + Dropped: 0 + + To manually continue having the trigger aggregate events, append + :cont instead. Notice that the trigger info displays as [active] + again, and the data has changed:: + + # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \ + /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist + # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active] + + { child_comm: dconf worker } hitcount: 1 + { child_comm: dconf worker } hitcount: 1 + { child_comm: kthreadd } hitcount: 1 + { child_comm: gdbus } hitcount: 1 + { child_comm: ibus-daemon } hitcount: 1 + { child_comm: Socket Thread } hitcount: 2 + { child_comm: evolution-alarm } hitcount: 2 + { child_comm: smbd } hitcount: 2 + { child_comm: whoopsie } hitcount: 3 + { child_comm: compiz } hitcount: 3 + { child_comm: evolution-sourc } hitcount: 4 + { child_comm: bash } hitcount: 5 + { child_comm: pool } hitcount: 5 + { child_comm: postgres } hitcount: 6 + { child_comm: firefox } hitcount: 8 + { child_comm: dhclient } hitcount: 11 + { child_comm: emacs } hitcount: 12 + { child_comm: dbus-daemon } hitcount: 22 + { child_comm: nm-dispatcher.a } hitcount: 22 + { child_comm: evolution } hitcount: 35 + { child_comm: glib-pacrunner } hitcount: 59 + + Totals: + Hits: 206 + Entries: 21 + Dropped: 0 + + The previous example showed how to start and stop a hist trigger by + appending 'pause' and 'continue' to the hist trigger command. A + hist trigger can also be started in a paused state by initially + starting the trigger with ':pause' appended. This allows you to + start the trigger only when you're ready to start collecting data + and not before. For example, you could start the trigger in a + paused state, then unpause it and do something you want to measure, + then pause the trigger again when done. + + Of course, doing this manually can be difficult and error-prone, but + it is possible to automatically start and stop a hist trigger based + on some condition, via the enable_hist and disable_hist triggers. + + For example, suppose we wanted to take a look at the relative + weights in terms of skb length for each callpath that leads to a + netif_receieve_skb event when downloading a decent-sized file using + wget. + + First we set up an initially paused stacktrace trigger on the + netif_receive_skb event:: + + # echo 'hist:key=stacktrace:vals=len:pause' > \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + + Next, we set up an 'enable_hist' trigger on the sched_process_exec + event, with an 'if filename==/usr/bin/wget' filter. The effect of + this new trigger is that it will 'unpause' the hist trigger we just + set up on netif_receive_skb if and only if it sees a + sched_process_exec event with a filename of '/usr/bin/wget'. When + that happens, all netif_receive_skb events are aggregated into a + hash table keyed on stacktrace:: + + # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger + + The aggregation continues until the netif_receive_skb is paused + again, which is what the following disable_hist event does by + creating a similar setup on the sched_process_exit event, using the + filter 'comm==wget':: + + # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger + + Whenever a process exits and the comm field of the disable_hist + trigger filter matches 'comm==wget', the netif_receive_skb hist + trigger is disabled. + + The overall effect is that netif_receive_skb events are aggregated + into the hash table for only the duration of the wget. Executing a + wget command and then listing the 'hist' file will display the + output generated by the wget command:: + + $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz + + # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist + # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused] + + { stacktrace: + __netif_receive_skb_core+0x46d/0x990 + __netif_receive_skb+0x18/0x60 + netif_receive_skb_internal+0x23/0x90 + napi_gro_receive+0xc8/0x100 + ieee80211_deliver_skb+0xd6/0x270 [mac80211] + ieee80211_rx_handlers+0xccf/0x22f0 [mac80211] + ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211] + ieee80211_rx+0x31d/0x900 [mac80211] + iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm] + iwl_rx_dispatch+0x8e/0xf0 [iwldvm] + iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi] + irq_thread_fn+0x20/0x50 + irq_thread+0x11f/0x150 + kthread+0xd2/0xf0 + ret_from_fork+0x42/0x70 + } hitcount: 85 len: 28884 + { stacktrace: + __netif_receive_skb_core+0x46d/0x990 + __netif_receive_skb+0x18/0x60 + netif_receive_skb_internal+0x23/0x90 + napi_gro_complete+0xa4/0xe0 + dev_gro_receive+0x23a/0x360 + napi_gro_receive+0x30/0x100 + ieee80211_deliver_skb+0xd6/0x270 [mac80211] + ieee80211_rx_handlers+0xccf/0x22f0 [mac80211] + ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211] + ieee80211_rx+0x31d/0x900 [mac80211] + iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm] + iwl_rx_dispatch+0x8e/0xf0 [iwldvm] + iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi] + irq_thread_fn+0x20/0x50 + irq_thread+0x11f/0x150 + kthread+0xd2/0xf0 + } hitcount: 98 len: 664329 + { stacktrace: + __netif_receive_skb_core+0x46d/0x990 + __netif_receive_skb+0x18/0x60 + process_backlog+0xa8/0x150 + net_rx_action+0x15d/0x340 + __do_softirq+0x114/0x2c0 + do_softirq_own_stack+0x1c/0x30 + do_softirq+0x65/0x70 + __local_bh_enable_ip+0xb5/0xc0 + ip_finish_output+0x1f4/0x840 + ip_output+0x6b/0xc0 + ip_local_out_sk+0x31/0x40 + ip_send_skb+0x1a/0x50 + udp_send_skb+0x173/0x2a0 + udp_sendmsg+0x2bf/0x9f0 + inet_sendmsg+0x64/0xa0 + sock_sendmsg+0x3d/0x50 + } hitcount: 115 len: 13030 + { stacktrace: + __netif_receive_skb_core+0x46d/0x990 + __netif_receive_skb+0x18/0x60 + netif_receive_skb_internal+0x23/0x90 + napi_gro_complete+0xa4/0xe0 + napi_gro_flush+0x6d/0x90 + iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi] + irq_thread_fn+0x20/0x50 + irq_thread+0x11f/0x150 + kthread+0xd2/0xf0 + ret_from_fork+0x42/0x70 + } hitcount: 934 len: 5512212 + + Totals: + Hits: 1232 + Entries: 4 + Dropped: 0 + + The above shows all the netif_receive_skb callpaths and their total + lengths for the duration of the wget command. + + The 'clear' hist trigger param can be used to clear the hash table. + Suppose we wanted to try another run of the previous example but + this time also wanted to see the complete list of events that went + into the histogram. In order to avoid having to set everything up + again, we can just clear the histogram first:: + + # echo 'hist:key=stacktrace:vals=len:clear' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + + Just to verify that it is in fact cleared, here's what we now see in + the hist file:: + + # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist + # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused] + + Totals: + Hits: 0 + Entries: 0 + Dropped: 0 + + Since we want to see the detailed list of every netif_receive_skb + event occurring during the new run, which are in fact the same + events being aggregated into the hash table, we add some additional + 'enable_event' events to the triggering sched_process_exec and + sched_process_exit events as such:: + + # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger + + # echo 'disable_event:net:netif_receive_skb if comm==wget' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger + + If you read the trigger files for the sched_process_exec and + sched_process_exit triggers, you should see two triggers for each: + one enabling/disabling the hist aggregation and the other + enabling/disabling the logging of events:: + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger + enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget + enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger + enable_event:net:netif_receive_skb:unlimited if comm==wget + disable_hist:net:netif_receive_skb:unlimited if comm==wget + + In other words, whenever either of the sched_process_exec or + sched_process_exit events is hit and matches 'wget', it enables or + disables both the histogram and the event log, and what you end up + with is a hash table and set of events just covering the specified + duration. Run the wget command again:: + + $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz + + Displaying the 'hist' file should show something similar to what you + saw in the last run, but this time you should also see the + individual events in the trace file:: + + # cat /sys/kernel/debug/tracing/trace + + # tracer: nop + # + # entries-in-buffer/entries-written: 183/1426 #P:4 + # + # _-----=> irqs-off + # / _----=> need-resched + # | / _---=> hardirq/softirq + # || / _--=> preempt-depth + # ||| / delay + # TASK-PID CPU# |||| TIMESTAMP FUNCTION + # | | | |||| | | + wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60 + wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60 + dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130 + dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138 + ##### CPU 2 buffer started #### + irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948 + irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500 + irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948 + irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948 + irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500 + . + . + . + + The following example demonstrates how multiple hist triggers can be + attached to a given event. This capability can be useful for + creating a set of different summaries derived from the same set of + events, or for comparing the effects of different filters, among + other things:: + + # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:keys=skbaddr.hex:vals=len' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:keys=len:vals=common_preempt_count' >> \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + + The above set of commands create four triggers differing only in + their filters, along with a completely different though fairly + nonsensical trigger. Note that in order to append multiple hist + triggers to the same file, you should use the '>>' operator to + append them ('>' will also add the new hist trigger, but will remove + any existing hist triggers beforehand). + + Displaying the contents of the 'hist' file for the event shows the + contents of all five histograms:: + + # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist + + # event histogram + # + # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active] + # + + { len: 176 } hitcount: 1 common_preempt_count: 0 + { len: 223 } hitcount: 1 common_preempt_count: 0 + { len: 4854 } hitcount: 1 common_preempt_count: 0 + { len: 395 } hitcount: 1 common_preempt_count: 0 + { len: 177 } hitcount: 1 common_preempt_count: 0 + { len: 446 } hitcount: 1 common_preempt_count: 0 + { len: 1601 } hitcount: 1 common_preempt_count: 0 + . + . + . + { len: 1280 } hitcount: 66 common_preempt_count: 0 + { len: 116 } hitcount: 81 common_preempt_count: 40 + { len: 708 } hitcount: 112 common_preempt_count: 0 + { len: 46 } hitcount: 221 common_preempt_count: 0 + { len: 1264 } hitcount: 458 common_preempt_count: 0 + + Totals: + Hits: 1428 + Entries: 147 + Dropped: 0 + + + # event histogram + # + # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] + # + + { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130 + { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280 + { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280 + { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115 + { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115 + { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46 + { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118 + { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60 + { skbaddr: ffff880100065900 } hitcount: 1 len: 46 + { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116 + { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280 + { skbaddr: ffff880100064700 } hitcount: 1 len: 365 + { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60 + . + . + . + { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677 + { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052 + { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589 + { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326 + { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678 + { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678 + { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589 + { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307 + { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032 + + Totals: + Hits: 1451 + Entries: 318 + Dropped: 0 + + + # event histogram + # + # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active] + # + + + Totals: + Hits: 0 + Entries: 0 + Dropped: 0 + + + # event histogram + # + # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active] + # + + { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212 + { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212 + { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212 + { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492 + { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212 + { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212 + { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854 + { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636 + { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924 + { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356 + { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420 + { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996 + + Totals: + Hits: 14 + Entries: 12 + Dropped: 0 + + + # event histogram + # + # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active] + # + + + Totals: + Hits: 0 + Entries: 0 + Dropped: 0 + + Named triggers can be used to have triggers share a common set of + histogram data. This capability is mostly useful for combining the + output of events generated by tracepoints contained inside inline + functions, but names can be used in a hist trigger on any event. + For example, these two triggers when hit will update the same 'len' + field in the shared 'foo' histogram data:: + + # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger + # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger + + You can see that they're updating common histogram data by reading + each event's hist files at the same time:: + + # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist; + cat /sys/kernel/debug/tracing/events/net/netif_rx/hist + + # event histogram + # + # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] + # + + { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46 + { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76 + { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468 + { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46 + { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52 + { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168 + { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260 + { skbaddr: ffff880064505000 } hitcount: 1 len: 46 + { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32 + { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46 + { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44 + { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168 + { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40 + { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40 + { skbaddr: ffff880064505f00 } hitcount: 1 len: 174 + { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160 + { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76 + { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32 + { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988 + { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46 + { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44 + { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676 + { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107 + { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92 + { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142 + { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220 + { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92 + { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92 + { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675 + { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138 + { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138 + { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184 + { skbaddr: ffff880064504400 } hitcount: 4 len: 184 + { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184 + { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230 + { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196 + { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276 + { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276 + + Totals: + Hits: 81 + Entries: 42 + Dropped: 0 + # event histogram + # + # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active] + # + + { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46 + { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76 + { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468 + { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46 + { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52 + { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168 + { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260 + { skbaddr: ffff880064505000 } hitcount: 1 len: 46 + { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32 + { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46 + { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44 + { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168 + { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40 + { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40 + { skbaddr: ffff880064505f00 } hitcount: 1 len: 174 + { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160 + { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76 + { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32 + { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46 + { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988 + { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46 + { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44 + { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676 + { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107 + { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92 + { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142 + { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220 + { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92 + { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92 + { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675 + { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138 + { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138 + { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184 + { skbaddr: ffff880064504400 } hitcount: 4 len: 184 + { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184 + { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230 + { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196 + { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276 + { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276 + + Totals: + Hits: 81 + Entries: 42 + Dropped: 0 + + And here's an example that shows how to combine histogram data from + any two events even if they don't share any 'compatible' fields + other than 'hitcount' and 'stacktrace'. These commands create a + couple of triggers named 'bar' using those fields:: + + # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \ + /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger + # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \ + /sys/kernel/debug/tracing/events/net/netif_rx/trigger + + And displaying the output of either shows some interesting if + somewhat confusing output:: + + # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist + # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist + + # event histogram + # + # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active] + # + + { stacktrace: + _do_fork+0x18e/0x330 + kernel_thread+0x29/0x30 + kthreadd+0x154/0x1b0 + ret_from_fork+0x3f/0x70 + } hitcount: 1 + { stacktrace: + netif_rx_internal+0xb2/0xd0 + netif_rx_ni+0x20/0x70 + dev_loopback_xmit+0xaa/0xd0 + ip_mc_output+0x126/0x240 + ip_local_out_sk+0x31/0x40 + igmp_send_report+0x1e9/0x230 + igmp_timer_expire+0xe9/0x120 + call_timer_fn+0x39/0xf0 + run_timer_softirq+0x1e1/0x290 + __do_softirq+0xfd/0x290 + irq_exit+0x98/0xb0 + smp_apic_timer_interrupt+0x4a/0x60 + apic_timer_interrupt+0x6d/0x80 + cpuidle_enter+0x17/0x20 + call_cpuidle+0x3b/0x60 + cpu_startup_entry+0x22d/0x310 + } hitcount: 1 + { stacktrace: + netif_rx_internal+0xb2/0xd0 + netif_rx_ni+0x20/0x70 + dev_loopback_xmit+0xaa/0xd0 + ip_mc_output+0x17f/0x240 + ip_local_out_sk+0x31/0x40 + ip_send_skb+0x1a/0x50 + udp_send_skb+0x13e/0x270 + udp_sendmsg+0x2bf/0x980 + inet_sendmsg+0x67/0xa0 + sock_sendmsg+0x38/0x50 + SYSC_sendto+0xef/0x170 + SyS_sendto+0xe/0x10 + entry_SYSCALL_64_fastpath+0x12/0x6a + } hitcount: 2 + { stacktrace: + netif_rx_internal+0xb2/0xd0 + netif_rx+0x1c/0x60 + loopback_xmit+0x6c/0xb0 + dev_hard_start_xmit+0x219/0x3a0 + __dev_queue_xmit+0x415/0x4f0 + dev_queue_xmit_sk+0x13/0x20 + ip_finish_output2+0x237/0x340 + ip_finish_output+0x113/0x1d0 + ip_output+0x66/0xc0 + ip_local_out_sk+0x31/0x40 + ip_send_skb+0x1a/0x50 + udp_send_skb+0x16d/0x270 + udp_sendmsg+0x2bf/0x980 + inet_sendmsg+0x67/0xa0 + sock_sendmsg+0x38/0x50 + ___sys_sendmsg+0x14e/0x270 + } hitcount: 76 + { stacktrace: + netif_rx_internal+0xb2/0xd0 + netif_rx+0x1c/0x60 + loopback_xmit+0x6c/0xb0 + dev_hard_start_xmit+0x219/0x3a0 + __dev_queue_xmit+0x415/0x4f0 + dev_queue_xmit_sk+0x13/0x20 + ip_finish_output2+0x237/0x340 + ip_finish_output+0x113/0x1d0 + ip_output+0x66/0xc0 + ip_local_out_sk+0x31/0x40 + ip_send_skb+0x1a/0x50 + udp_send_skb+0x16d/0x270 + udp_sendmsg+0x2bf/0x980 + inet_sendmsg+0x67/0xa0 + sock_sendmsg+0x38/0x50 + ___sys_sendmsg+0x269/0x270 + } hitcount: 77 + { stacktrace: + netif_rx_internal+0xb2/0xd0 + netif_rx+0x1c/0x60 + loopback_xmit+0x6c/0xb0 + dev_hard_start_xmit+0x219/0x3a0 + __dev_queue_xmit+0x415/0x4f0 + dev_queue_xmit_sk+0x13/0x20 + ip_finish_output2+0x237/0x340 + ip_finish_output+0x113/0x1d0 + ip_output+0x66/0xc0 + ip_local_out_sk+0x31/0x40 + ip_send_skb+0x1a/0x50 + udp_send_skb+0x16d/0x270 + udp_sendmsg+0x2bf/0x980 + inet_sendmsg+0x67/0xa0 + sock_sendmsg+0x38/0x50 + SYSC_sendto+0xef/0x170 + } hitcount: 88 + { stacktrace: + _do_fork+0x18e/0x330 + SyS_clone+0x19/0x20 + entry_SYSCALL_64_fastpath+0x12/0x6a + } hitcount: 244 + + Totals: + Hits: 489 + Entries: 7 + Dropped: 0 + +2.2 Inter-event hist triggers +----------------------------- + +Inter-event hist triggers are hist triggers that combine values from +one or more other events and create a histogram using that data. Data +from an inter-event histogram can in turn become the source for +further combined histograms, thus providing a chain of related +histograms, which is important for some applications. + +The most important example of an inter-event quantity that can be used +in this manner is latency, which is simply a difference in timestamps +between two events. Although latency is the most important +inter-event quantity, note that because the support is completely +general across the trace event subsystem, any event field can be used +in an inter-event quantity. + +An example of a histogram that combines data from other histograms +into a useful chain would be a 'wakeupswitch latency' histogram that +combines a 'wakeup latency' histogram and a 'switch latency' +histogram. + +Normally, a hist trigger specification consists of a (possibly +compound) key along with one or more numeric values, which are +continually updated sums associated with that key. A histogram +specification in this case consists of individual key and value +specifications that refer to trace event fields associated with a +single event type. + +The inter-event hist trigger extension allows fields from multiple +events to be referenced and combined into a multi-event histogram +specification. In support of this overall goal, a few enabling +features have been added to the hist trigger support: + + - In order to compute an inter-event quantity, a value from one + event needs to saved and then referenced from another event. This + requires the introduction of support for histogram 'variables'. + + - The computation of inter-event quantities and their combination + require some minimal amount of support for applying simple + expressions to variables (+ and -). + + - A histogram consisting of inter-event quantities isn't logically a + histogram on either event (so having the 'hist' file for either + event host the histogram output doesn't really make sense). To + address the idea that the histogram is associated with a + combination of events, support is added allowing the creation of + 'synthetic' events that are events derived from other events. + These synthetic events are full-fledged events just like any other + and can be used as such, as for instance to create the + 'combination' histograms mentioned previously. + + - A set of 'actions' can be associated with histogram entries - + these can be used to generate the previously mentioned synthetic + events, but can also be used for other purposes, such as for + example saving context when a 'max' latency has been hit. + + - Trace events don't have a 'timestamp' associated with them, but + there is an implicit timestamp saved along with an event in the + underlying ftrace ring buffer. This timestamp is now exposed as a + a synthetic field named 'common_timestamp' which can be used in + histograms as if it were any other event field; it isn't an actual + field in the trace format but rather is a synthesized value that + nonetheless can be used as if it were an actual field. By default + it is in units of nanoseconds; appending '.usecs' to a + common_timestamp field changes the units to microseconds. + +A note on inter-event timestamps: If common_timestamp is used in a +histogram, the trace buffer is automatically switched over to using +absolute timestamps and the "global" trace clock, in order to avoid +bogus timestamp differences with other clocks that aren't coherent +across CPUs. This can be overridden by specifying one of the other +trace clocks instead, using the "clock=XXX" hist trigger attribute, +where XXX is any of the clocks listed in the tracing/trace_clock +pseudo-file. + +These features are described in more detail in the following sections. + +2.2.1 Histogram Variables +------------------------- + +Variables are simply named locations used for saving and retrieving +values between matching events. A 'matching' event is defined as an +event that has a matching key - if a variable is saved for a histogram +entry corresponding to that key, any subsequent event with a matching +key can access that variable. + +A variable's value is normally available to any subsequent event until +it is set to something else by a subsequent event. The one exception +to that rule is that any variable used in an expression is essentially +'read-once' - once it's used by an expression in a subsequent event, +it's reset to its 'unset' state, which means it can't be used again +unless it's set again. This ensures not only that an event doesn't +use an uninitialized variable in a calculation, but that that variable +is used only once and not for any unrelated subsequent match. + +The basic syntax for saving a variable is to simply prefix a unique +variable name not corresponding to any keyword along with an '=' sign +to any event field. + +Either keys or values can be saved and retrieved in this way. This +creates a variable named 'ts0' for a histogram entry with the key +'next_pid':: + + # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ... >> \ + event/trigger + +The ts0 variable can be accessed by any subsequent event having the +same pid as 'next_pid'. + +Variable references are formed by prepending the variable name with +the '$' sign. Thus for example, the ts0 variable above would be +referenced as '$ts0' in expressions. + +Because 'vals=' is used, the common_timestamp variable value above +will also be summed as a normal histogram value would (though for a +timestamp it makes little sense). + +The below shows that a key value can also be saved in the same way:: + + # echo 'hist:timer_pid=common_pid:key=timer_pid ...' >> event/trigger + +If a variable isn't a key variable or prefixed with 'vals=', the +associated event field will be saved in a variable but won't be summed +as a value:: + + # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger + +Multiple variables can be assigned at the same time. The below would +result in both ts0 and b being created as variables, with both +common_timestamp and field1 additionally being summed as values:: + + # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \ + event/trigger + +Note that variable assignments can appear either preceding or +following their use. The command below behaves identically to the +command above:: + + # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \ + event/trigger + +Any number of variables not bound to a 'vals=' prefix can also be +assigned by simply separating them with colons. Below is the same +thing but without the values being summed in the histogram:: + + # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger + +Variables set as above can be referenced and used in expressions on +another event. + +For example, here's how a latency can be calculated:: + + # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger + # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger + +In the first line above, the event's timetamp is saved into the +variable ts0. In the next line, ts0 is subtracted from the second +event's timestamp to produce the latency, which is then assigned into +yet another variable, 'wakeup_lat'. The hist trigger below in turn +makes use of the wakeup_lat variable to compute a combined latency +using the same key and variable from yet another event:: + + # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger + +2.2.2 Synthetic Events +---------------------- + +Synthetic events are user-defined events generated from hist trigger +variables or fields associated with one or more other events. Their +purpose is to provide a mechanism for displaying data spanning +multiple events consistent with the existing and already familiar +usage for normal events. + +To define a synthetic event, the user writes a simple specification +consisting of the name of the new event along with one or more +variables and their types, which can be any valid field type, +separated by semicolons, to the tracing/synthetic_events file. + +For instance, the following creates a new event named 'wakeup_latency' +with 3 fields: lat, pid, and prio. Each of those fields is simply a +variable reference to a variable on another event:: + + # echo 'wakeup_latency \ + u64 lat; \ + pid_t pid; \ + int prio' >> \ + /sys/kernel/debug/tracing/synthetic_events + +Reading the tracing/synthetic_events file lists all the currently +defined synthetic events, in this case the event defined above:: + + # cat /sys/kernel/debug/tracing/synthetic_events + wakeup_latency u64 lat; pid_t pid; int prio + +An existing synthetic event definition can be removed by prepending +the command that defined it with a '!':: + + # echo '!wakeup_latency u64 lat pid_t pid int prio' >> \ + /sys/kernel/debug/tracing/synthetic_events + +At this point, there isn't yet an actual 'wakeup_latency' event +instantiated in the event subsytem - for this to happen, a 'hist +trigger action' needs to be instantiated and bound to actual fields +and variables defined on other events (see Section 2.2.3 below on +how that is done using hist trigger 'onmatch' action). Once that is +done, the 'wakeup_latency' synthetic event instance is created. + +A histogram can now be defined for the new synthetic event:: + + # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \ + /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger + +The new event is created under the tracing/events/synthetic/ directory +and looks and behaves just like any other event:: + + # ls /sys/kernel/debug/tracing/events/synthetic/wakeup_latency + enable filter format hist id trigger + +Like any other event, once a histogram is enabled for the event, the +output can be displayed by reading the event's 'hist' file. + +2.2.3 Hist trigger 'actions' +---------------------------- + +A hist trigger 'action' is a function that's executed whenever a +histogram entry is added or updated. + +The default 'action' if no special function is explicity specified is +as it always has been, to simply update the set of values associated +with an entry. Some applications, however, may want to perform +additional actions at that point, such as generate another event, or +compare and save a maximum. + +The following additional actions are available. To specify an action +for a given event, simply specify the action between colons in the +hist trigger specification. + + - onmatch(matching.event).<synthetic_event_name>(param list) + + The 'onmatch(matching.event).<synthetic_event_name>(params)' hist + trigger action is invoked whenever an event matches and the + histogram entry would be added or updated. It causes the named + synthetic event to be generated with the values given in the + 'param list'. The result is the generation of a synthetic event + that consists of the values contained in those variables at the + time the invoking event was hit. + + The 'param list' consists of one or more parameters which may be + either variables or fields defined on either the 'matching.event' + or the target event. The variables or fields specified in the + param list may be either fully-qualified or unqualified. If a + variable is specified as unqualified, it must be unique between + the two events. A field name used as a param can be unqualified + if it refers to the target event, but must be fully qualified if + it refers to the matching event. A fully-qualified name is of the + form 'system.event_name.$var_name' or 'system.event_name.field'. + + The 'matching.event' specification is simply the fully qualified + event name of the event that matches the target event for the + onmatch() functionality, in the form 'system.event_name'. + + Finally, the number and type of variables/fields in the 'param + list' must match the number and types of the fields in the + synthetic event being generated. + + As an example the below defines a simple synthetic event and uses + a variable defined on the sched_wakeup_new event as a parameter + when invoking the synthetic event. Here we define the synthetic + event:: + + # echo 'wakeup_new_test pid_t pid' >> \ + /sys/kernel/debug/tracing/synthetic_events + + # cat /sys/kernel/debug/tracing/synthetic_events + wakeup_new_test pid_t pid + + The following hist trigger both defines the missing testpid + variable and specifies an onmatch() action that generates a + wakeup_new_test synthetic event whenever a sched_wakeup_new event + occurs, which because of the 'if comm == "cyclictest"' filter only + happens when the executable is cyclictest:: + + # echo 'hist:keys=$testpid:testpid=pid:onmatch(sched.sched_wakeup_new).\ + wakeup_new_test($testpid) if comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger + + Creating and displaying a histogram based on those events is now + just a matter of using the fields and new synthetic event in the + tracing/events/synthetic directory, as usual:: + + # echo 'hist:keys=pid:sort=pid' >> \ + /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger + + Running 'cyclictest' should cause wakeup_new events to generate + wakeup_new_test synthetic events which should result in histogram + output in the wakeup_new_test event's hist file:: + + # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/hist + + A more typical usage would be to use two events to calculate a + latency. The following example uses a set of hist triggers to + produce a 'wakeup_latency' histogram. + + First, we define a 'wakeup_latency' synthetic event:: + + # echo 'wakeup_latency u64 lat; pid_t pid; int prio' >> \ + /sys/kernel/debug/tracing/synthetic_events + + Next, we specify that whenever we see a sched_waking event for a + cyclictest thread, save the timestamp in a 'ts0' variable:: + + # echo 'hist:keys=$saved_pid:saved_pid=pid:ts0=common_timestamp.usecs \ + if comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_waking/trigger + + Then, when the corresponding thread is actually scheduled onto the + CPU by a sched_switch event, calculate the latency and use that + along with another variable and an event field to generate a + wakeup_latency synthetic event:: + + # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\ + onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\ + $saved_pid,next_prio) if next_comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_switch/trigger + + We also need to create a histogram on the wakeup_latency synthetic + event in order to aggregate the generated synthetic event data:: + + # echo 'hist:keys=pid,prio,lat:sort=pid,lat' >> \ + /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger + + Finally, once we've run cyclictest to actually generate some + events, we can see the output by looking at the wakeup_latency + synthetic event's hist file:: + + # cat /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/hist + + - onmax(var).save(field,.. .) + + The 'onmax(var).save(field,...)' hist trigger action is invoked + whenever the value of 'var' associated with a histogram entry + exceeds the current maximum contained in that variable. + + The end result is that the trace event fields specified as the + onmax.save() params will be saved if 'var' exceeds the current + maximum for that hist trigger entry. This allows context from the + event that exhibited the new maximum to be saved for later + reference. When the histogram is displayed, additional fields + displaying the saved values will be printed. + + As an example the below defines a couple of hist triggers, one for + sched_waking and another for sched_switch, keyed on pid. Whenever + a sched_waking occurs, the timestamp is saved in the entry + corresponding to the current pid, and when the scheduler switches + back to that pid, the timestamp difference is calculated. If the + resulting latency, stored in wakeup_lat, exceeds the current + maximum latency, the values specified in the save() fields are + recorded:: + + # echo 'hist:keys=pid:ts0=common_timestamp.usecs \ + if comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_waking/trigger + + # echo 'hist:keys=next_pid:\ + wakeup_lat=common_timestamp.usecs-$ts0:\ + onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) \ + if next_comm=="cyclictest"' >> \ + /sys/kernel/debug/tracing/events/sched/sched_switch/trigger + + When the histogram is displayed, the max value and the saved + values corresponding to the max are displayed following the rest + of the fields:: + + # cat /sys/kernel/debug/tracing/events/sched/sched_switch/hist + { next_pid: 2255 } hitcount: 239 + common_timestamp-ts0: 0 + max: 27 + next_comm: cyclictest + prev_pid: 0 prev_prio: 120 prev_comm: swapper/1 + + { next_pid: 2256 } hitcount: 2355 + common_timestamp-ts0: 0 + max: 49 next_comm: cyclictest + prev_pid: 0 prev_prio: 120 prev_comm: swapper/0 + + Totals: + Hits: 12970 + Entries: 2 + Dropped: 0 + +3. User space creating a trigger +-------------------------------- + +Writing into /sys/kernel/tracing/trace_marker writes into the ftrace +ring buffer. This can also act like an event, by writing into the trigger +file located in /sys/kernel/tracing/events/ftrace/print/ + +Modifying cyclictest to write into the trace_marker file before it sleeps +and after it wakes up, something like this:: + + static void traceputs(char *str) + { + /* tracemark_fd is the trace_marker file descriptor */ + if (tracemark_fd < 0) + return; + /* write the tracemark message */ + write(tracemark_fd, str, strlen(str)); + } + +And later add something like:: + + traceputs("start"); + clock_nanosleep(...); + traceputs("end"); + +We can make a histogram from this:: + + # cd /sys/kernel/tracing + # echo 'latency u64 lat' > synthetic_events + # echo 'hist:keys=common_pid:ts0=common_timestamp.usecs if buf == "start"' > events/ftrace/print/trigger + # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(ftrace.print).latency($lat) if buf == "end"' >> events/ftrace/print/trigger + # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger + +The above created a synthetic event called "latency" and two histograms +against the trace_marker, one gets triggered when "start" is written into the +trace_marker file and the other when "end" is written. If the pids match, then +it will call the "latency" synthetic event with the calculated latency as its +parameter. Finally, a histogram is added to the latency synthetic event to +record the calculated latency along with the pid. + +Now running cyclictest with:: + + # ./cyclictest -p80 -d0 -i250 -n -a -t --tracemark -b 1000 + + -p80 : run threads at priority 80 + -d0 : have all threads run at the same interval + -i250 : start the interval at 250 microseconds (all threads will do this) + -n : sleep with nanosleep + -a : affine all threads to a separate CPU + -t : one thread per available CPU + --tracemark : enable trace mark writing + -b 1000 : stop if any latency is greater than 1000 microseconds + +Note, the -b 1000 is used just to make --tracemark available. + +Then we can see the histogram created by this with:: + + # cat events/synthetic/latency/hist + # event histogram + # + # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active] + # + + { lat: 107, common_pid: 2039 } hitcount: 1 + { lat: 122, common_pid: 2041 } hitcount: 1 + { lat: 166, common_pid: 2039 } hitcount: 1 + { lat: 174, common_pid: 2039 } hitcount: 1 + { lat: 194, common_pid: 2041 } hitcount: 1 + { lat: 196, common_pid: 2036 } hitcount: 1 + { lat: 197, common_pid: 2038 } hitcount: 1 + { lat: 198, common_pid: 2039 } hitcount: 1 + { lat: 199, common_pid: 2039 } hitcount: 1 + { lat: 200, common_pid: 2041 } hitcount: 1 + { lat: 201, common_pid: 2039 } hitcount: 2 + { lat: 202, common_pid: 2038 } hitcount: 1 + { lat: 202, common_pid: 2043 } hitcount: 1 + { lat: 203, common_pid: 2039 } hitcount: 1 + { lat: 203, common_pid: 2036 } hitcount: 1 + { lat: 203, common_pid: 2041 } hitcount: 1 + { lat: 206, common_pid: 2038 } hitcount: 2 + { lat: 207, common_pid: 2039 } hitcount: 1 + { lat: 207, common_pid: 2036 } hitcount: 1 + { lat: 208, common_pid: 2040 } hitcount: 1 + { lat: 209, common_pid: 2043 } hitcount: 1 + { lat: 210, common_pid: 2039 } hitcount: 1 + { lat: 211, common_pid: 2039 } hitcount: 4 + { lat: 212, common_pid: 2043 } hitcount: 1 + { lat: 212, common_pid: 2039 } hitcount: 2 + { lat: 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common_pid: 2036 } hitcount: 135 + { lat: 248, common_pid: 2039 } hitcount: 26 + { lat: 248, common_pid: 2041 } hitcount: 503 + { lat: 248, common_pid: 2043 } hitcount: 66 + { lat: 248, common_pid: 2040 } hitcount: 46 + { lat: 249, common_pid: 2037 } hitcount: 29 + { lat: 249, common_pid: 2038 } hitcount: 1 + { lat: 249, common_pid: 2043 } hitcount: 29 + { lat: 249, common_pid: 2039 } hitcount: 8 + { lat: 249, common_pid: 2042 } hitcount: 56 + { lat: 249, common_pid: 2040 } hitcount: 27 + { lat: 249, common_pid: 2041 } hitcount: 11 + { lat: 249, common_pid: 2036 } hitcount: 27 + { lat: 250, common_pid: 2038 } hitcount: 1 + { lat: 250, common_pid: 2036 } hitcount: 30 + { lat: 250, common_pid: 2040 } hitcount: 19 + { lat: 250, common_pid: 2043 } hitcount: 22 + { lat: 250, common_pid: 2042 } hitcount: 20 + { lat: 250, common_pid: 2041 } hitcount: 1 + { lat: 250, common_pid: 2039 } hitcount: 6 + { lat: 250, common_pid: 2037 } hitcount: 48 + { lat: 251, common_pid: 2037 } hitcount: 43 + { lat: 251, common_pid: 2039 } hitcount: 1 + { lat: 251, common_pid: 2036 } hitcount: 12 + { lat: 251, common_pid: 2042 } hitcount: 2 + { lat: 251, common_pid: 2041 } hitcount: 1 + { lat: 251, common_pid: 2043 } hitcount: 15 + { lat: 251, common_pid: 2040 } hitcount: 3 + { lat: 252, common_pid: 2040 } hitcount: 1 + { lat: 252, common_pid: 2036 } hitcount: 12 + { lat: 252, common_pid: 2037 } hitcount: 21 + { lat: 252, common_pid: 2043 } hitcount: 14 + { lat: 253, common_pid: 2037 } hitcount: 21 + { lat: 253, common_pid: 2039 } hitcount: 2 + { lat: 253, common_pid: 2036 } hitcount: 9 + { lat: 253, common_pid: 2043 } hitcount: 6 + { lat: 253, common_pid: 2040 } hitcount: 1 + { lat: 254, common_pid: 2036 } hitcount: 8 + { lat: 254, common_pid: 2043 } hitcount: 3 + { lat: 254, common_pid: 2041 } hitcount: 1 + { lat: 254, common_pid: 2042 } hitcount: 1 + { lat: 254, common_pid: 2039 } hitcount: 1 + { lat: 254, common_pid: 2037 } hitcount: 12 + { lat: 255, common_pid: 2043 } hitcount: 1 + { lat: 255, common_pid: 2037 } hitcount: 2 + { lat: 255, common_pid: 2036 } hitcount: 2 + { lat: 255, common_pid: 2039 } hitcount: 8 + { lat: 256, common_pid: 2043 } hitcount: 1 + { lat: 256, common_pid: 2036 } hitcount: 4 + { lat: 256, common_pid: 2039 } hitcount: 6 + { lat: 257, common_pid: 2039 } hitcount: 5 + { lat: 257, common_pid: 2036 } hitcount: 4 + { lat: 258, common_pid: 2039 } hitcount: 5 + { lat: 258, common_pid: 2036 } hitcount: 2 + { lat: 259, common_pid: 2036 } hitcount: 7 + { lat: 259, common_pid: 2039 } hitcount: 7 + { lat: 260, common_pid: 2036 } hitcount: 8 + { lat: 260, common_pid: 2039 } hitcount: 6 + { lat: 261, common_pid: 2036 } hitcount: 5 + { lat: 261, common_pid: 2039 } hitcount: 7 + { lat: 262, common_pid: 2039 } hitcount: 5 + { lat: 262, common_pid: 2036 } hitcount: 5 + { lat: 263, common_pid: 2039 } hitcount: 7 + { lat: 263, common_pid: 2036 } hitcount: 7 + { lat: 264, common_pid: 2039 } hitcount: 9 + { lat: 264, common_pid: 2036 } hitcount: 9 + { lat: 265, common_pid: 2036 } hitcount: 5 + { lat: 265, common_pid: 2039 } hitcount: 1 + { lat: 266, common_pid: 2036 } hitcount: 1 + { lat: 266, common_pid: 2039 } hitcount: 3 + { lat: 267, common_pid: 2036 } hitcount: 1 + { lat: 267, common_pid: 2039 } hitcount: 3 + { lat: 268, common_pid: 2036 } hitcount: 1 + { lat: 268, common_pid: 2039 } hitcount: 6 + { lat: 269, common_pid: 2036 } hitcount: 1 + { lat: 269, common_pid: 2043 } hitcount: 1 + { lat: 269, common_pid: 2039 } hitcount: 2 + { lat: 270, common_pid: 2040 } hitcount: 1 + { lat: 270, common_pid: 2039 } hitcount: 6 + { lat: 271, common_pid: 2041 } hitcount: 1 + { lat: 271, common_pid: 2039 } hitcount: 5 + { lat: 272, common_pid: 2039 } hitcount: 10 + { lat: 273, common_pid: 2039 } hitcount: 8 + { lat: 274, common_pid: 2039 } hitcount: 2 + { lat: 275, common_pid: 2039 } hitcount: 1 + { lat: 276, common_pid: 2039 } hitcount: 2 + { lat: 276, common_pid: 2037 } hitcount: 1 + { lat: 276, common_pid: 2038 } hitcount: 1 + { lat: 277, common_pid: 2039 } hitcount: 1 + { lat: 277, common_pid: 2042 } hitcount: 1 + { lat: 278, common_pid: 2039 } hitcount: 1 + { lat: 279, common_pid: 2039 } hitcount: 4 + { lat: 279, common_pid: 2043 } hitcount: 1 + { lat: 280, common_pid: 2039 } hitcount: 3 + { lat: 283, common_pid: 2036 } hitcount: 2 + { lat: 284, common_pid: 2039 } hitcount: 1 + { lat: 284, common_pid: 2043 } hitcount: 1 + { lat: 288, common_pid: 2039 } hitcount: 1 + { lat: 289, common_pid: 2039 } hitcount: 1 + { lat: 300, common_pid: 2039 } hitcount: 1 + { lat: 384, common_pid: 2039 } hitcount: 1 + + Totals: + Hits: 67625 + Entries: 278 + Dropped: 0 + +Note, the writes are around the sleep, so ideally they will all be of 250 +microseconds. If you are wondering how there are several that are under +250 microseconds, that is because the way cyclictest works, is if one +iteration comes in late, the next one will set the timer to wake up less that +250. That is, if an iteration came in 50 microseconds late, the next wake up +will be at 200 microseconds. + +But this could easily be done in userspace. To make this even more +interesting, we can mix the histogram between events that happened in the +kernel with trace_marker:: + + # cd /sys/kernel/tracing + # echo 'latency u64 lat' > synthetic_events + # echo 'hist:keys=pid:ts0=common_timestamp.usecs' > events/sched/sched_waking/trigger + # echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$ts0:onmatch(sched.sched_waking).latency($lat) if buf == "end"' > events/ftrace/print/trigger + # echo 'hist:keys=lat,common_pid:sort=lat' > events/synthetic/latency/trigger + +The difference this time is that instead of using the trace_marker to start +the latency, the sched_waking event is used, matching the common_pid for the +trace_marker write with the pid that is being woken by sched_waking. + +After running cyclictest again with the same parameters, we now have:: + + # cat events/synthetic/latency/hist + # event histogram + # + # trigger info: hist:keys=lat,common_pid:vals=hitcount:sort=lat:size=2048 [active] + # + + { lat: 7, common_pid: 2302 } hitcount: 640 + { lat: 7, common_pid: 2299 } hitcount: 42 + { lat: 7, common_pid: 2303 } hitcount: 18 + { lat: 7, common_pid: 2305 } hitcount: 166 + { lat: 7, common_pid: 2306 } hitcount: 1 + { lat: 7, common_pid: 2301 } hitcount: 91 + { lat: 7, common_pid: 2300 } hitcount: 17 + { lat: 8, common_pid: 2303 } hitcount: 8296 + { lat: 8, common_pid: 2304 } hitcount: 6864 + { lat: 8, common_pid: 2305 } hitcount: 9464 + { lat: 8, common_pid: 2301 } hitcount: 9213 + { lat: 8, common_pid: 2306 } hitcount: 6246 + { lat: 8, common_pid: 2302 } hitcount: 8797 + { lat: 8, common_pid: 2299 } hitcount: 8771 + { lat: 8, common_pid: 2300 } hitcount: 8119 + { lat: 9, common_pid: 2305 } hitcount: 1519 + { lat: 9, common_pid: 2299 } hitcount: 2346 + { lat: 9, common_pid: 2303 } hitcount: 2841 + { lat: 9, common_pid: 2301 } hitcount: 1846 + { lat: 9, common_pid: 2304 } hitcount: 3861 + { lat: 9, common_pid: 2302 } hitcount: 1210 + { lat: 9, common_pid: 2300 } hitcount: 2762 + { lat: 9, common_pid: 2306 } hitcount: 4247 + { lat: 10, common_pid: 2299 } hitcount: 16 + { lat: 10, common_pid: 2306 } hitcount: 333 + { lat: 10, common_pid: 2303 } hitcount: 16 + { lat: 10, common_pid: 2304 } hitcount: 168 + { lat: 10, common_pid: 2302 } hitcount: 240 + { lat: 10, common_pid: 2301 } hitcount: 28 + { lat: 10, common_pid: 2300 } hitcount: 95 + { lat: 10, common_pid: 2305 } hitcount: 18 + { lat: 11, common_pid: 2303 } hitcount: 5 + { lat: 11, common_pid: 2305 } hitcount: 8 + { lat: 11, common_pid: 2306 } hitcount: 221 + { lat: 11, common_pid: 2302 } hitcount: 76 + { lat: 11, common_pid: 2304 } hitcount: 26 + { lat: 11, common_pid: 2300 } hitcount: 125 + { lat: 11, common_pid: 2299 } hitcount: 2 + { lat: 12, common_pid: 2305 } hitcount: 3 + { lat: 12, common_pid: 2300 } hitcount: 6 + { lat: 12, common_pid: 2306 } hitcount: 90 + { lat: 12, common_pid: 2302 } hitcount: 4 + { lat: 12, common_pid: 2303 } hitcount: 1 + { lat: 12, common_pid: 2304 } hitcount: 122 + { lat: 13, common_pid: 2300 } hitcount: 12 + { lat: 13, common_pid: 2301 } hitcount: 1 + { lat: 13, common_pid: 2306 } hitcount: 32 + { lat: 13, common_pid: 2302 } hitcount: 5 + { lat: 13, common_pid: 2305 } hitcount: 1 + { lat: 13, common_pid: 2303 } hitcount: 1 + { lat: 13, common_pid: 2304 } hitcount: 61 + { lat: 14, common_pid: 2303 } hitcount: 4 + { lat: 14, common_pid: 2306 } hitcount: 5 + { lat: 14, common_pid: 2305 } hitcount: 4 + { lat: 14, common_pid: 2304 } hitcount: 62 + { lat: 14, common_pid: 2302 } hitcount: 19 + { lat: 14, common_pid: 2300 } hitcount: 33 + { lat: 14, common_pid: 2299 } hitcount: 1 + { lat: 14, common_pid: 2301 } hitcount: 4 + { lat: 15, common_pid: 2305 } hitcount: 1 + { lat: 15, common_pid: 2302 } hitcount: 25 + { lat: 15, common_pid: 2300 } hitcount: 11 + { lat: 15, common_pid: 2299 } hitcount: 5 + { lat: 15, common_pid: 2301 } hitcount: 1 + { lat: 15, common_pid: 2304 } hitcount: 8 + { lat: 15, common_pid: 2303 } hitcount: 1 + { lat: 15, common_pid: 2306 } hitcount: 6 + { lat: 16, common_pid: 2302 } hitcount: 31 + { lat: 16, common_pid: 2306 } hitcount: 3 + { lat: 16, common_pid: 2300 } hitcount: 5 + { lat: 17, common_pid: 2302 } hitcount: 6 + { lat: 17, common_pid: 2303 } hitcount: 1 + { lat: 18, common_pid: 2304 } hitcount: 1 + { lat: 18, common_pid: 2302 } hitcount: 8 + { lat: 18, common_pid: 2299 } hitcount: 1 + { lat: 18, common_pid: 2301 } hitcount: 1 + { lat: 19, common_pid: 2303 } hitcount: 4 + { lat: 19, common_pid: 2304 } hitcount: 5 + { lat: 19, common_pid: 2302 } hitcount: 4 + { lat: 19, common_pid: 2299 } hitcount: 3 + { lat: 19, common_pid: 2306 } hitcount: 1 + { lat: 19, common_pid: 2300 } hitcount: 4 + { lat: 19, common_pid: 2305 } hitcount: 5 + { lat: 20, common_pid: 2299 } hitcount: 2 + { lat: 20, common_pid: 2302 } hitcount: 3 + { lat: 20, common_pid: 2305 } hitcount: 1 + { lat: 20, common_pid: 2300 } hitcount: 2 + { lat: 20, common_pid: 2301 } hitcount: 2 + { lat: 20, common_pid: 2303 } hitcount: 3 + { lat: 21, common_pid: 2305 } hitcount: 1 + { lat: 21, common_pid: 2299 } hitcount: 5 + { lat: 21, common_pid: 2303 } hitcount: 4 + { lat: 21, common_pid: 2302 } hitcount: 7 + { lat: 21, common_pid: 2300 } hitcount: 1 + { lat: 21, common_pid: 2301 } hitcount: 5 + { lat: 21, common_pid: 2304 } hitcount: 2 + { lat: 22, common_pid: 2302 } hitcount: 5 + { lat: 22, common_pid: 2303 } hitcount: 1 + { lat: 22, common_pid: 2306 } hitcount: 3 + { lat: 22, common_pid: 2301 } hitcount: 2 + { lat: 22, common_pid: 2300 } hitcount: 1 + { lat: 22, common_pid: 2299 } hitcount: 1 + { lat: 22, common_pid: 2305 } hitcount: 1 + { lat: 22, common_pid: 2304 } hitcount: 1 + { lat: 23, common_pid: 2299 } hitcount: 1 + { lat: 23, common_pid: 2306 } hitcount: 2 + { lat: 23, common_pid: 2302 } hitcount: 6 + { lat: 24, common_pid: 2302 } hitcount: 3 + { lat: 24, common_pid: 2300 } hitcount: 1 + { lat: 24, common_pid: 2306 } hitcount: 2 + { lat: 24, common_pid: 2305 } hitcount: 1 + { lat: 24, common_pid: 2299 } hitcount: 1 + { lat: 25, common_pid: 2300 } hitcount: 1 + { lat: 25, common_pid: 2302 } hitcount: 4 + { lat: 26, common_pid: 2302 } hitcount: 2 + { lat: 27, common_pid: 2305 } hitcount: 1 + { lat: 27, common_pid: 2300 } hitcount: 1 + { lat: 27, common_pid: 2302 } hitcount: 3 + { lat: 28, common_pid: 2306 } hitcount: 1 + { lat: 28, common_pid: 2302 } hitcount: 4 + { lat: 29, common_pid: 2302 } hitcount: 1 + { lat: 29, common_pid: 2300 } hitcount: 2 + { lat: 29, common_pid: 2306 } hitcount: 1 + { lat: 29, common_pid: 2304 } hitcount: 1 + { lat: 30, common_pid: 2302 } hitcount: 4 + { lat: 31, common_pid: 2302 } hitcount: 6 + { lat: 32, common_pid: 2302 } hitcount: 1 + { lat: 33, common_pid: 2299 } hitcount: 1 + { lat: 33, common_pid: 2302 } hitcount: 3 + { lat: 34, common_pid: 2302 } hitcount: 2 + { lat: 35, common_pid: 2302 } hitcount: 1 + { lat: 35, common_pid: 2304 } hitcount: 1 + { lat: 36, common_pid: 2302 } hitcount: 4 + { lat: 37, common_pid: 2302 } hitcount: 6 + { lat: 38, common_pid: 2302 } hitcount: 2 + { lat: 39, common_pid: 2302 } hitcount: 2 + { lat: 39, common_pid: 2304 } hitcount: 1 + { lat: 40, common_pid: 2304 } hitcount: 2 + { lat: 40, common_pid: 2302 } hitcount: 5 + { lat: 41, common_pid: 2304 } hitcount: 1 + { lat: 41, common_pid: 2302 } hitcount: 8 + { lat: 42, common_pid: 2302 } hitcount: 6 + { lat: 42, common_pid: 2304 } hitcount: 1 + { lat: 43, common_pid: 2302 } hitcount: 3 + { lat: 43, common_pid: 2304 } hitcount: 4 + { lat: 44, common_pid: 2302 } hitcount: 6 + { lat: 45, common_pid: 2302 } hitcount: 5 + { lat: 46, common_pid: 2302 } hitcount: 5 + { lat: 47, common_pid: 2302 } hitcount: 7 + { lat: 48, common_pid: 2301 } hitcount: 1 + { lat: 48, common_pid: 2302 } hitcount: 9 + { lat: 49, common_pid: 2302 } hitcount: 3 + { lat: 50, common_pid: 2302 } hitcount: 1 + { lat: 50, common_pid: 2301 } hitcount: 1 + { lat: 51, common_pid: 2302 } hitcount: 2 + { lat: 51, common_pid: 2301 } hitcount: 1 + { lat: 61, common_pid: 2302 } hitcount: 1 + { lat: 110, common_pid: 2302 } hitcount: 1 + + Totals: + Hits: 89565 + Entries: 158 + Dropped: 0 + +This doesn't tell us any information about how late cyclictest may have +woken up, but it does show us a nice histogram of how long it took from +the time that cyclictest was woken to the time it made it into user space. diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst new file mode 100644 index 000000000..573934964 --- /dev/null +++ b/Documentation/trace/hwlat_detector.rst @@ -0,0 +1,83 @@ +========================= +Hardware Latency Detector +========================= + +Introduction +------------- + +The tracer hwlat_detector is a special purpose tracer that is used to +detect large system latencies induced by the behavior of certain underlying +hardware or firmware, independent of Linux itself. The code was developed +originally to detect SMIs (System Management Interrupts) on x86 systems, +however there is nothing x86 specific about this patchset. It was +originally written for use by the "RT" patch since the Real Time +kernel is highly latency sensitive. + +SMIs are not serviced by the Linux kernel, which means that it does not +even know that they are occuring. SMIs are instead set up by BIOS code +and are serviced by BIOS code, usually for "critical" events such as +management of thermal sensors and fans. Sometimes though, SMIs are used for +other tasks and those tasks can spend an inordinate amount of time in the +handler (sometimes measured in milliseconds). Obviously this is a problem if +you are trying to keep event service latencies down in the microsecond range. + +The hardware latency detector works by hogging one of the cpus for configurable +amounts of time (with interrupts disabled), polling the CPU Time Stamp Counter +for some period, then looking for gaps in the TSC data. Any gap indicates a +time when the polling was interrupted and since the interrupts are disabled, +the only thing that could do that would be an SMI or other hardware hiccup +(or an NMI, but those can be tracked). + +Note that the hwlat detector should *NEVER* be used in a production environment. +It is intended to be run manually to determine if the hardware platform has a +problem with long system firmware service routines. + +Usage +------ + +Write the ASCII text "hwlat" into the current_tracer file of the tracing system +(mounted at /sys/kernel/tracing or /sys/kernel/tracing). It is possible to +redefine the threshold in microseconds (us) above which latency spikes will +be taken into account. + +Example:: + + # echo hwlat > /sys/kernel/tracing/current_tracer + # echo 100 > /sys/kernel/tracing/tracing_thresh + +The /sys/kernel/tracing/hwlat_detector interface contains the following files: + + - width - time period to sample with CPUs held (usecs) + must be less than the total window size (enforced) + - window - total period of sampling, width being inside (usecs) + +By default the width is set to 500,000 and window to 1,000,000, meaning that +for every 1,000,000 usecs (1s) the hwlat detector will spin for 500,000 usecs +(0.5s). If tracing_thresh contains zero when hwlat tracer is enabled, it will +change to a default of 10 usecs. If any latencies that exceed the threshold is +observed then the data will be written to the tracing ring buffer. + +The minimum sleep time between periods is 1 millisecond. Even if width +is less than 1 millisecond apart from window, to allow the system to not +be totally starved. + +If tracing_thresh was zero when hwlat detector was started, it will be set +back to zero if another tracer is loaded. Note, the last value in +tracing_thresh that hwlat detector had will be saved and this value will +be restored in tracing_thresh if it is still zero when hwlat detector is +started again. + +The following tracing directory files are used by the hwlat_detector: + +in /sys/kernel/tracing: + + - tracing_threshold - minimum latency value to be considered (usecs) + - tracing_max_latency - maximum hardware latency actually observed (usecs) + - tracing_cpumask - the CPUs to move the hwlat thread across + - hwlat_detector/width - specified amount of time to spin within window (usecs) + - hwlat_detector/window - amount of time between (width) runs (usecs) + +The hwlat detector's kernel thread will migrate across each CPU specified in +tracing_cpumask between each window. To limit the migration, either modify +tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU +affinity directly, and the migration will stop. diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst new file mode 100644 index 000000000..306997941 --- /dev/null +++ b/Documentation/trace/index.rst @@ -0,0 +1,24 @@ +========================== +Linux Tracing Technologies +========================== + +.. toctree:: + :maxdepth: 2 + + ftrace-design + tracepoint-analysis + ftrace + ftrace-uses + kprobetrace + uprobetracer + tracepoints + events + events-kmem + events-power + events-nmi + events-msr + mmiotrace + histogram + hwlat_detector + intel_th + stm diff --git a/Documentation/trace/intel_th.rst b/Documentation/trace/intel_th.rst new file mode 100644 index 000000000..19e2d633f --- /dev/null +++ b/Documentation/trace/intel_th.rst @@ -0,0 +1,122 @@ +======================= +Intel(R) Trace Hub (TH) +======================= + +Overview +-------- + +Intel(R) Trace Hub (TH) is a set of hardware blocks that produce, +switch and output trace data from multiple hardware and software +sources over several types of trace output ports encoded in System +Trace Protocol (MIPI STPv2) and is intended to perform full system +debugging. For more information on the hardware, see Intel(R) Trace +Hub developer's manual [1]. + +It consists of trace sources, trace destinations (outputs) and a +switch (Global Trace Hub, GTH). These devices are placed on a bus of +their own ("intel_th"), where they can be discovered and configured +via sysfs attributes. + +Currently, the following Intel TH subdevices (blocks) are supported: + - Software Trace Hub (STH), trace source, which is a System Trace + Module (STM) device, + - Memory Storage Unit (MSU), trace output, which allows storing + trace hub output in system memory, + - Parallel Trace Interface output (PTI), trace output to an external + debug host via a PTI port, + - Global Trace Hub (GTH), which is a switch and a central component + of Intel(R) Trace Hub architecture. + +Common attributes for output devices are described in +Documentation/ABI/testing/sysfs-bus-intel_th-output-devices, the most +notable of them is "active", which enables or disables trace output +into that particular output device. + +GTH allows directing different STP masters into different output ports +via its "masters" attribute group. More detailed GTH interface +description is at Documentation/ABI/testing/sysfs-bus-intel_th-devices-gth. + +STH registers an stm class device, through which it provides interface +to userspace and kernelspace software trace sources. See +Documentation/trace/stm.rst for more information on that. + +MSU can be configured to collect trace data into a system memory +buffer, which can later on be read from its device nodes via read() or +mmap() interface. + +On the whole, Intel(R) Trace Hub does not require any special +userspace software to function; everything can be configured, started +and collected via sysfs attributes, and device nodes. + +[1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf + +Bus and Subdevices +------------------ + +For each Intel TH device in the system a bus of its own is +created and assigned an id number that reflects the order in which TH +devices were emumerated. All TH subdevices (devices on intel_th bus) +begin with this id: 0-gth, 0-msc0, 0-msc1, 0-pti, 0-sth, which is +followed by device's name and an optional index. + +Output devices also get a device node in /dev/intel_thN, where N is +the Intel TH device id. For example, MSU's memory buffers, when +allocated, are accessible via /dev/intel_th0/msc{0,1}. + +Quick example +------------- + +# figure out which GTH port is the first memory controller:: + + $ cat /sys/bus/intel_th/devices/0-msc0/port + 0 + +# looks like it's port 0, configure master 33 to send data to port 0:: + + $ echo 0 > /sys/bus/intel_th/devices/0-gth/masters/33 + +# allocate a 2-windowed multiblock buffer on the first memory +# controller, each with 64 pages:: + + $ echo multi > /sys/bus/intel_th/devices/0-msc0/mode + $ echo 64,64 > /sys/bus/intel_th/devices/0-msc0/nr_pages + +# enable wrapping for this controller, too:: + + $ echo 1 > /sys/bus/intel_th/devices/0-msc0/wrap + +# and enable tracing into this port:: + + $ echo 1 > /sys/bus/intel_th/devices/0-msc0/active + +# .. send data to master 33, see stm.txt for more details .. +# .. wait for traces to pile up .. +# .. and stop the trace:: + + $ echo 0 > /sys/bus/intel_th/devices/0-msc0/active + +# and now you can collect the trace from the device node:: + + $ cat /dev/intel_th0/msc0 > my_stp_trace + +Host Debugger Mode +------------------ + +It is possible to configure the Trace Hub and control its trace +capture from a remote debug host, which should be connected via one of +the hardware debugging interfaces, which will then be used to both +control Intel Trace Hub and transfer its trace data to the debug host. + +The driver needs to be told that such an arrangement is taking place +so that it does not touch any capture/port configuration and avoids +conflicting with the debug host's configuration accesses. The only +activity that the driver will perform in this mode is collecting +software traces to the Software Trace Hub (an stm class device). The +user is still responsible for setting up adequate master/channel +mappings that the decoder on the receiving end would recognize. + +In order to enable the host mode, set the 'host_mode' parameter of the +'intel_th' kernel module to 'y'. None of the virtual output devices +will show up on the intel_th bus. Also, trace configuration and +capture controlling attribute groups of the 'gth' device will not be +exposed. The 'sth' device will operate as usual. diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst new file mode 100644 index 000000000..8bfc75c90 --- /dev/null +++ b/Documentation/trace/kprobetrace.rst @@ -0,0 +1,193 @@ +========================== +Kprobe-based Event Tracing +========================== + +:Author: Masami Hiramatsu + +Overview +-------- +These events are similar to tracepoint based events. Instead of Tracepoint, +this is based on kprobes (kprobe and kretprobe). So it can probe wherever +kprobes can probe (this means, all functions except those with +__kprobes/nokprobe_inline annotation and those marked NOKPROBE_SYMBOL). +Unlike the Tracepoint based event, this can be added and removed +dynamically, on the fly. + +To enable this feature, build your kernel with CONFIG_KPROBE_EVENTS=y. + +Similar to the events tracer, this doesn't need to be activated via +current_tracer. Instead of that, add probe points via +/sys/kernel/debug/tracing/kprobe_events, and enable it via +/sys/kernel/debug/tracing/events/kprobes/<EVENT>/enable. + + +Synopsis of kprobe_events +------------------------- +:: + + p[:[GRP/]EVENT] [MOD:]SYM[+offs]|MEMADDR [FETCHARGS] : Set a probe + r[MAXACTIVE][:[GRP/]EVENT] [MOD:]SYM[+0] [FETCHARGS] : Set a return probe + -:[GRP/]EVENT : Clear a probe + + GRP : Group name. If omitted, use "kprobes" for it. + EVENT : Event name. If omitted, the event name is generated + based on SYM+offs or MEMADDR. + MOD : Module name which has given SYM. + SYM[+offs] : Symbol+offset where the probe is inserted. + MEMADDR : Address where the probe is inserted. + MAXACTIVE : Maximum number of instances of the specified function that + can be probed simultaneously, or 0 for the default value + as defined in Documentation/kprobes.txt section 1.3.1. + + FETCHARGS : Arguments. Each probe can have up to 128 args. + %REG : Fetch register REG + @ADDR : Fetch memory at ADDR (ADDR should be in kernel) + @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol) + $stackN : Fetch Nth entry of stack (N >= 0) + $stack : Fetch stack address. + $retval : Fetch return value.(*) + $comm : Fetch current task comm. + +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**) + NAME=FETCHARG : Set NAME as the argument name of FETCHARG. + FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types + (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types + (x8/x16/x32/x64), "string" and bitfield are supported. + + (*) only for return probe. + (**) this is useful for fetching a field of data structures. + +Types +----- +Several types are supported for fetch-args. Kprobe tracer will access memory +by given type. Prefix 's' and 'u' means those types are signed and unsigned +respectively. 'x' prefix implies it is unsigned. Traced arguments are shown +in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32' +or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and +x86-64 uses x64). +String type is a special type, which fetches a "null-terminated" string from +kernel space. This means it will fail and store NULL if the string container +has been paged out. +Bitfield is another special type, which takes 3 parameters, bit-width, bit- +offset, and container-size (usually 32). The syntax is:: + + b<bit-width>@<bit-offset>/<container-size> + +For $comm, the default type is "string"; any other type is invalid. + + +Per-Probe Event Filtering +------------------------- +Per-probe event filtering feature allows you to set different filter on each +probe and gives you what arguments will be shown in trace buffer. If an event +name is specified right after 'p:' or 'r:' in kprobe_events, it adds an event +under tracing/events/kprobes/<EVENT>, at the directory you can see 'id', +'enable', 'format', 'filter' and 'trigger'. + +enable: + You can enable/disable the probe by writing 1 or 0 on it. + +format: + This shows the format of this probe event. + +filter: + You can write filtering rules of this event. + +id: + This shows the id of this probe event. + +trigger: + This allows to install trigger commands which are executed when the event is + hit (for details, see Documentation/trace/events.rst, section 6). + +Event Profiling +--------------- +You can check the total number of probe hits and probe miss-hits via +/sys/kernel/debug/tracing/kprobe_profile. +The first column is event name, the second is the number of probe hits, +the third is the number of probe miss-hits. + + +Usage examples +-------------- +To add a probe as a new event, write a new definition to kprobe_events +as below:: + + echo 'p:myprobe do_sys_open dfd=%ax filename=%dx flags=%cx mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events + +This sets a kprobe on the top of do_sys_open() function with recording +1st to 4th arguments as "myprobe" event. Note, which register/stack entry is +assigned to each function argument depends on arch-specific ABI. If you unsure +the ABI, please try to use probe subcommand of perf-tools (you can find it +under tools/perf/). +As this example shows, users can choose more familiar names for each arguments. +:: + + echo 'r:myretprobe do_sys_open $retval' >> /sys/kernel/debug/tracing/kprobe_events + +This sets a kretprobe on the return point of do_sys_open() function with +recording return value as "myretprobe" event. +You can see the format of these events via +/sys/kernel/debug/tracing/events/kprobes/<EVENT>/format. +:: + + cat /sys/kernel/debug/tracing/events/kprobes/myprobe/format + name: myprobe + ID: 780 + format: + field:unsigned short common_type; offset:0; size:2; signed:0; + field:unsigned char common_flags; offset:2; size:1; signed:0; + field:unsigned char common_preempt_count; offset:3; size:1;signed:0; + field:int common_pid; offset:4; size:4; signed:1; + + field:unsigned long __probe_ip; offset:12; size:4; signed:0; + field:int __probe_nargs; offset:16; size:4; signed:1; + field:unsigned long dfd; offset:20; size:4; signed:0; + field:unsigned long filename; offset:24; size:4; signed:0; + field:unsigned long flags; offset:28; size:4; signed:0; + field:unsigned long mode; offset:32; size:4; signed:0; + + + print fmt: "(%lx) dfd=%lx filename=%lx flags=%lx mode=%lx", REC->__probe_ip, + REC->dfd, REC->filename, REC->flags, REC->mode + +You can see that the event has 4 arguments as in the expressions you specified. +:: + + echo > /sys/kernel/debug/tracing/kprobe_events + +This clears all probe points. + +Or, +:: + + echo -:myprobe >> kprobe_events + +This clears probe points selectively. + +Right after definition, each event is disabled by default. For tracing these +events, you need to enable it. +:: + + echo 1 > /sys/kernel/debug/tracing/events/kprobes/myprobe/enable + echo 1 > /sys/kernel/debug/tracing/events/kprobes/myretprobe/enable + +And you can see the traced information via /sys/kernel/debug/tracing/trace. +:: + + cat /sys/kernel/debug/tracing/trace + # tracer: nop + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + <...>-1447 [001] 1038282.286875: myprobe: (do_sys_open+0x0/0xd6) dfd=3 filename=7fffd1ec4440 flags=8000 mode=0 + <...>-1447 [001] 1038282.286878: myretprobe: (sys_openat+0xc/0xe <- do_sys_open) $retval=fffffffffffffffe + <...>-1447 [001] 1038282.286885: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=40413c flags=8000 mode=1b6 + <...>-1447 [001] 1038282.286915: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 + <...>-1447 [001] 1038282.286969: myprobe: (do_sys_open+0x0/0xd6) dfd=ffffff9c filename=4041c6 flags=98800 mode=10 + <...>-1447 [001] 1038282.286976: myretprobe: (sys_open+0x1b/0x1d <- do_sys_open) $retval=3 + + +Each line shows when the kernel hits an event, and <- SYMBOL means kernel +returns from SYMBOL(e.g. "sys_open+0x1b/0x1d <- do_sys_open" means kernel +returns from do_sys_open to sys_open+0x1b). + diff --git a/Documentation/trace/mmiotrace.rst b/Documentation/trace/mmiotrace.rst new file mode 100644 index 000000000..5116e8ca2 --- /dev/null +++ b/Documentation/trace/mmiotrace.rst @@ -0,0 +1,184 @@ +=================================== +In-kernel memory-mapped I/O tracing +=================================== + + +Home page and links to optional user space tools: + + http://nouveau.freedesktop.org/wiki/MmioTrace + +MMIO tracing was originally developed by Intel around 2003 for their Fault +Injection Test Harness. In Dec 2006 - Jan 2007, using the code from Intel, +Jeff Muizelaar created a tool for tracing MMIO accesses with the Nouveau +project in mind. Since then many people have contributed. + +Mmiotrace was built for reverse engineering any memory-mapped IO device with +the Nouveau project as the first real user. Only x86 and x86_64 architectures +are supported. + +Out-of-tree mmiotrace was originally modified for mainline inclusion and +ftrace framework by Pekka Paalanen <pq@iki.fi>. + + +Preparation +----------- + +Mmiotrace feature is compiled in by the CONFIG_MMIOTRACE option. Tracing is +disabled by default, so it is safe to have this set to yes. SMP systems are +supported, but tracing is unreliable and may miss events if more than one CPU +is on-line, therefore mmiotrace takes all but one CPU off-line during run-time +activation. You can re-enable CPUs by hand, but you have been warned, there +is no way to automatically detect if you are losing events due to CPUs racing. + + +Usage Quick Reference +--------------------- +:: + + $ mount -t debugfs debugfs /sys/kernel/debug + $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer + $ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & + Start X or whatever. + $ echo "X is up" > /sys/kernel/debug/tracing/trace_marker + $ echo nop > /sys/kernel/debug/tracing/current_tracer + Check for lost events. + + +Usage +----- + +Make sure debugfs is mounted to /sys/kernel/debug. +If not (requires root privileges):: + + $ mount -t debugfs debugfs /sys/kernel/debug + +Check that the driver you are about to trace is not loaded. + +Activate mmiotrace (requires root privileges):: + + $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer + +Start storing the trace:: + + $ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt & + +The 'cat' process should stay running (sleeping) in the background. + +Load the driver you want to trace and use it. Mmiotrace will only catch MMIO +accesses to areas that are ioremapped while mmiotrace is active. + +During tracing you can place comments (markers) into the trace by +$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker +This makes it easier to see which part of the (huge) trace corresponds to +which action. It is recommended to place descriptive markers about what you +do. + +Shut down mmiotrace (requires root privileges):: + + $ echo nop > /sys/kernel/debug/tracing/current_tracer + +The 'cat' process exits. If it does not, kill it by issuing 'fg' command and +pressing ctrl+c. + +Check that mmiotrace did not lose events due to a buffer filling up. Either:: + + $ grep -i lost mydump.txt + +which tells you exactly how many events were lost, or use:: + + $ dmesg + +to view your kernel log and look for "mmiotrace has lost events" warning. If +events were lost, the trace is incomplete. You should enlarge the buffers and +try again. Buffers are enlarged by first seeing how large the current buffers +are:: + + $ cat /sys/kernel/debug/tracing/buffer_size_kb + +gives you a number. Approximately double this number and write it back, for +instance:: + + $ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb + +Then start again from the top. + +If you are doing a trace for a driver project, e.g. Nouveau, you should also +do the following before sending your results:: + + $ lspci -vvv > lspci.txt + $ dmesg > dmesg.txt + $ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt + +and then send the .tar.gz file. The trace compresses considerably. Replace +"pciid" and "nick" with the PCI ID or model name of your piece of hardware +under investigation and your nickname. + + +How Mmiotrace Works +------------------- + +Access to hardware IO-memory is gained by mapping addresses from PCI bus by +calling one of the ioremap_*() functions. Mmiotrace is hooked into the +__ioremap() function and gets called whenever a mapping is created. Mapping is +an event that is recorded into the trace log. Note that ISA range mappings +are not caught, since the mapping always exists and is returned directly. + +MMIO accesses are recorded via page faults. Just before __ioremap() returns, +the mapped pages are marked as not present. Any access to the pages causes a +fault. The page fault handler calls mmiotrace to handle the fault. Mmiotrace +marks the page present, sets TF flag to achieve single stepping and exits the +fault handler. The instruction that faulted is executed and debug trap is +entered. Here mmiotrace again marks the page as not present. The instruction +is decoded to get the type of operation (read/write), data width and the value +read or written. These are stored to the trace log. + +Setting the page present in the page fault handler has a race condition on SMP +machines. During the single stepping other CPUs may run freely on that page +and events can be missed without a notice. Re-enabling other CPUs during +tracing is discouraged. + + +Trace Log Format +---------------- + +The raw log is text and easily filtered with e.g. grep and awk. One record is +one line in the log. A record starts with a keyword, followed by keyword- +dependent arguments. Arguments are separated by a space, or continue until the +end of line. The format for version 20070824 is as follows: + +Explanation Keyword Space-separated arguments +--------------------------------------------------------------------------- + +read event R width, timestamp, map id, physical, value, PC, PID +write event W width, timestamp, map id, physical, value, PC, PID +ioremap event MAP timestamp, map id, physical, virtual, length, PC, PID +iounmap event UNMAP timestamp, map id, PC, PID +marker MARK timestamp, text +version VERSION the string "20070824" +info for reader LSPCI one line from lspci -v +PCI address map PCIDEV space-separated /proc/bus/pci/devices data +unk. opcode UNKNOWN timestamp, map id, physical, data, PC, PID + +Timestamp is in seconds with decimals. Physical is a PCI bus address, virtual +is a kernel virtual address. Width is the data width in bytes and value is the +data value. Map id is an arbitrary id number identifying the mapping that was +used in an operation. PC is the program counter and PID is process id. PC is +zero if it is not recorded. PID is always zero as tracing MMIO accesses +originating in user space memory is not yet supported. + +For instance, the following awk filter will pass all 32-bit writes that target +physical addresses in the range [0xfb73ce40, 0xfb800000] +:: + + $ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 && + adr < 0xfb800000) print; }' + + +Tools for Developers +-------------------- + +The user space tools include utilities for: + - replacing numeric addresses and values with hardware register names + - replaying MMIO logs, i.e., re-executing the recorded writes + + diff --git a/Documentation/trace/postprocess/decode_msr.py b/Documentation/trace/postprocess/decode_msr.py new file mode 100644 index 000000000..aa9cc7abd --- /dev/null +++ b/Documentation/trace/postprocess/decode_msr.py @@ -0,0 +1,37 @@ +#!/usr/bin/env python +# add symbolic names to read_msr / write_msr in trace +# decode_msr msr-index.h < trace +import sys +import re + +msrs = dict() + +with open(sys.argv[1] if len(sys.argv) > 1 else "msr-index.h", "r") as f: + for j in f: + m = re.match(r'#define (MSR_\w+)\s+(0x[0-9a-fA-F]+)', j) + if m: + msrs[int(m.group(2), 16)] = m.group(1) + +extra_ranges = ( + ( "MSR_LASTBRANCH_%d_FROM_IP", 0x680, 0x69F ), + ( "MSR_LASTBRANCH_%d_TO_IP", 0x6C0, 0x6DF ), + ( "LBR_INFO_%d", 0xdc0, 0xddf ), +) + +for j in sys.stdin: + m = re.search(r'(read|write)_msr:\s+([0-9a-f]+)', j) + if m: + r = None + num = int(m.group(2), 16) + if num in msrs: + r = msrs[num] + else: + for er in extra_ranges: + if er[1] <= num <= er[2]: + r = er[0] % (num - er[1],) + break + if r: + j = j.replace(" " + m.group(2), " " + r + "(" + m.group(2) + ")") + print j, + + diff --git a/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl b/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl new file mode 100644 index 000000000..b9b7d80c2 --- /dev/null +++ b/Documentation/trace/postprocess/trace-pagealloc-postprocess.pl @@ -0,0 +1,418 @@ +#!/usr/bin/env perl +# This is a POC (proof of concept or piece of crap, take your pick) for reading the +# text representation of trace output related to page allocation. It makes an attempt +# to extract some high-level information on what is going on. The accuracy of the parser +# may vary considerably +# +# Example usage: trace-pagealloc-postprocess.pl < /sys/kernel/debug/tracing/trace_pipe +# other options +# --prepend-parent Report on the parent proc and PID +# --read-procstat If the trace lacks process info, get it from /proc +# --ignore-pid Aggregate processes of the same name together +# +# Copyright (c) IBM Corporation 2009 +# Author: Mel Gorman <mel@csn.ul.ie> +use strict; +use Getopt::Long; + +# Tracepoint events +use constant MM_PAGE_ALLOC => 1; +use constant MM_PAGE_FREE => 2; +use constant MM_PAGE_FREE_BATCHED => 3; +use constant MM_PAGE_PCPU_DRAIN => 4; +use constant MM_PAGE_ALLOC_ZONE_LOCKED => 5; +use constant MM_PAGE_ALLOC_EXTFRAG => 6; +use constant EVENT_UNKNOWN => 7; + +# Constants used to track state +use constant STATE_PCPU_PAGES_DRAINED => 8; +use constant STATE_PCPU_PAGES_REFILLED => 9; + +# High-level events extrapolated from tracepoints +use constant HIGH_PCPU_DRAINS => 10; +use constant HIGH_PCPU_REFILLS => 11; +use constant HIGH_EXT_FRAGMENT => 12; +use constant HIGH_EXT_FRAGMENT_SEVERE => 13; +use constant HIGH_EXT_FRAGMENT_MODERATE => 14; +use constant HIGH_EXT_FRAGMENT_CHANGED => 15; + +my %perprocesspid; +my %perprocess; +my $opt_ignorepid; +my $opt_read_procstat; +my $opt_prepend_parent; + +# Catch sigint and exit on request +my $sigint_report = 0; +my $sigint_exit = 0; +my $sigint_pending = 0; +my $sigint_received = 0; +sub sigint_handler { + my $current_time = time; + if ($current_time - 2 > $sigint_received) { + print "SIGINT received, report pending. Hit ctrl-c again to exit\n"; + $sigint_report = 1; + } else { + if (!$sigint_exit) { + print "Second SIGINT received quickly, exiting\n"; + } + $sigint_exit++; + } + + if ($sigint_exit > 3) { + print "Many SIGINTs received, exiting now without report\n"; + exit; + } + + $sigint_received = $current_time; + $sigint_pending = 1; +} +$SIG{INT} = "sigint_handler"; + +# Parse command line options +GetOptions( + 'ignore-pid' => \$opt_ignorepid, + 'read-procstat' => \$opt_read_procstat, + 'prepend-parent' => \$opt_prepend_parent, +); + +# Defaults for dynamically discovered regex's +my $regex_fragdetails_default = 'page=([0-9a-f]*) pfn=([0-9]*) alloc_order=([-0-9]*) fallback_order=([-0-9]*) pageblock_order=([-0-9]*) alloc_migratetype=([-0-9]*) fallback_migratetype=([-0-9]*) fragmenting=([-0-9]) change_ownership=([-0-9])'; + +# Dyanically discovered regex +my $regex_fragdetails; + +# Static regex used. Specified like this for readability and for use with /o +# (process_pid) (cpus ) ( time ) (tpoint ) (details) +my $regex_traceevent = '\s*([a-zA-Z0-9-]*)\s*(\[[0-9]*\])\s*([0-9.]*):\s*([a-zA-Z_]*):\s*(.*)'; +my $regex_statname = '[-0-9]*\s\((.*)\).*'; +my $regex_statppid = '[-0-9]*\s\(.*\)\s[A-Za-z]\s([0-9]*).*'; + +sub generate_traceevent_regex { + my $event = shift; + my $default = shift; + my $regex; + + # Read the event format or use the default + if (!open (FORMAT, "/sys/kernel/debug/tracing/events/$event/format")) { + $regex = $default; + } else { + my $line; + while (!eof(FORMAT)) { + $line = <FORMAT>; + if ($line =~ /^print fmt:\s"(.*)",.*/) { + $regex = $1; + $regex =~ s/%p/\([0-9a-f]*\)/g; + $regex =~ s/%d/\([-0-9]*\)/g; + $regex =~ s/%lu/\([0-9]*\)/g; + } + } + } + + # Verify fields are in the right order + my $tuple; + foreach $tuple (split /\s/, $regex) { + my ($key, $value) = split(/=/, $tuple); + my $expected = shift; + if ($key ne $expected) { + print("WARNING: Format not as expected '$key' != '$expected'"); + $regex =~ s/$key=\((.*)\)/$key=$1/; + } + } + + if (defined shift) { + die("Fewer fields than expected in format"); + } + + return $regex; +} +$regex_fragdetails = generate_traceevent_regex("kmem/mm_page_alloc_extfrag", + $regex_fragdetails_default, + "page", "pfn", + "alloc_order", "fallback_order", "pageblock_order", + "alloc_migratetype", "fallback_migratetype", + "fragmenting", "change_ownership"); + +sub read_statline($) { + my $pid = $_[0]; + my $statline; + + if (open(STAT, "/proc/$pid/stat")) { + $statline = <STAT>; + close(STAT); + } + + if ($statline eq '') { + $statline = "-1 (UNKNOWN_PROCESS_NAME) R 0"; + } + + return $statline; +} + +sub guess_process_pid($$) { + my $pid = $_[0]; + my $statline = $_[1]; + + if ($pid == 0) { + return "swapper-0"; + } + + if ($statline !~ /$regex_statname/o) { + die("Failed to math stat line for process name :: $statline"); + } + return "$1-$pid"; +} + +sub parent_info($$) { + my $pid = $_[0]; + my $statline = $_[1]; + my $ppid; + + if ($pid == 0) { + return "NOPARENT-0"; + } + + if ($statline !~ /$regex_statppid/o) { + die("Failed to match stat line process ppid:: $statline"); + } + + # Read the ppid stat line + $ppid = $1; + return guess_process_pid($ppid, read_statline($ppid)); +} + +sub process_events { + my $traceevent; + my $process_pid; + my $cpus; + my $timestamp; + my $tracepoint; + my $details; + my $statline; + + # Read each line of the event log +EVENT_PROCESS: + while ($traceevent = <STDIN>) { + if ($traceevent =~ /$regex_traceevent/o) { + $process_pid = $1; + $tracepoint = $4; + + if ($opt_read_procstat || $opt_prepend_parent) { + $process_pid =~ /(.*)-([0-9]*)$/; + my $process = $1; + my $pid = $2; + + $statline = read_statline($pid); + + if ($opt_read_procstat && $process eq '') { + $process_pid = guess_process_pid($pid, $statline); + } + + if ($opt_prepend_parent) { + $process_pid = parent_info($pid, $statline) . " :: $process_pid"; + } + } + + # Unnecessary in this script. Uncomment if required + # $cpus = $2; + # $timestamp = $3; + } else { + next; + } + + # Perl Switch() sucks majorly + if ($tracepoint eq "mm_page_alloc") { + $perprocesspid{$process_pid}->{MM_PAGE_ALLOC}++; + } elsif ($tracepoint eq "mm_page_free") { + $perprocesspid{$process_pid}->{MM_PAGE_FREE}++ + } elsif ($tracepoint eq "mm_page_free_batched") { + $perprocesspid{$process_pid}->{MM_PAGE_FREE_BATCHED}++; + } elsif ($tracepoint eq "mm_page_pcpu_drain") { + $perprocesspid{$process_pid}->{MM_PAGE_PCPU_DRAIN}++; + $perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED}++; + } elsif ($tracepoint eq "mm_page_alloc_zone_locked") { + $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED}++; + $perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED}++; + } elsif ($tracepoint eq "mm_page_alloc_extfrag") { + + # Extract the details of the event now + $details = $5; + + my ($page, $pfn); + my ($alloc_order, $fallback_order, $pageblock_order); + my ($alloc_migratetype, $fallback_migratetype); + my ($fragmenting, $change_ownership); + + if ($details !~ /$regex_fragdetails/o) { + print "WARNING: Failed to parse mm_page_alloc_extfrag as expected\n"; + next; + } + + $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG}++; + $page = $1; + $pfn = $2; + $alloc_order = $3; + $fallback_order = $4; + $pageblock_order = $5; + $alloc_migratetype = $6; + $fallback_migratetype = $7; + $fragmenting = $8; + $change_ownership = $9; + + if ($fragmenting) { + $perprocesspid{$process_pid}->{HIGH_EXT_FRAG}++; + if ($fallback_order <= 3) { + $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE}++; + } else { + $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE}++; + } + } + if ($change_ownership) { + $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED}++; + } + } else { + $perprocesspid{$process_pid}->{EVENT_UNKNOWN}++; + } + + # Catch a full pcpu drain event + if ($perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED} && + $tracepoint ne "mm_page_pcpu_drain") { + + $perprocesspid{$process_pid}->{HIGH_PCPU_DRAINS}++; + $perprocesspid{$process_pid}->{STATE_PCPU_PAGES_DRAINED} = 0; + } + + # Catch a full pcpu refill event + if ($perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED} && + $tracepoint ne "mm_page_alloc_zone_locked") { + $perprocesspid{$process_pid}->{HIGH_PCPU_REFILLS}++; + $perprocesspid{$process_pid}->{STATE_PCPU_PAGES_REFILLED} = 0; + } + + if ($sigint_pending) { + last EVENT_PROCESS; + } + } +} + +sub dump_stats { + my $hashref = shift; + my %stats = %$hashref; + + # Dump per-process stats + my $process_pid; + my $max_strlen = 0; + + # Get the maximum process name + foreach $process_pid (keys %perprocesspid) { + my $len = length($process_pid); + if ($len > $max_strlen) { + $max_strlen = $len; + } + } + $max_strlen += 2; + + printf("\n"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s\n", + "Process", "Pages", "Pages", "Pages", "Pages", "PCPU", "PCPU", "PCPU", "Fragment", "Fragment", "MigType", "Fragment", "Fragment", "Unknown"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s\n", + "details", "allocd", "allocd", "freed", "freed", "pages", "drains", "refills", "Fallback", "Causing", "Changed", "Severe", "Moderate", ""); + + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s %8s\n", + "", "", "under lock", "direct", "pagevec", "drain", "", "", "", "", "", "", "", ""); + + foreach $process_pid (keys %stats) { + # Dump final aggregates + if ($stats{$process_pid}->{STATE_PCPU_PAGES_DRAINED}) { + $stats{$process_pid}->{HIGH_PCPU_DRAINS}++; + $stats{$process_pid}->{STATE_PCPU_PAGES_DRAINED} = 0; + } + if ($stats{$process_pid}->{STATE_PCPU_PAGES_REFILLED}) { + $stats{$process_pid}->{HIGH_PCPU_REFILLS}++; + $stats{$process_pid}->{STATE_PCPU_PAGES_REFILLED} = 0; + } + + printf("%-" . $max_strlen . "s %8d %10d %8d %8d %8d %8d %8d %8d %8d %8d %8d %8d %8d\n", + $process_pid, + $stats{$process_pid}->{MM_PAGE_ALLOC}, + $stats{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED}, + $stats{$process_pid}->{MM_PAGE_FREE}, + $stats{$process_pid}->{MM_PAGE_FREE_BATCHED}, + $stats{$process_pid}->{MM_PAGE_PCPU_DRAIN}, + $stats{$process_pid}->{HIGH_PCPU_DRAINS}, + $stats{$process_pid}->{HIGH_PCPU_REFILLS}, + $stats{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG}, + $stats{$process_pid}->{HIGH_EXT_FRAG}, + $stats{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED}, + $stats{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE}, + $stats{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE}, + $stats{$process_pid}->{EVENT_UNKNOWN}); + } +} + +sub aggregate_perprocesspid() { + my $process_pid; + my $process; + undef %perprocess; + + foreach $process_pid (keys %perprocesspid) { + $process = $process_pid; + $process =~ s/-([0-9])*$//; + if ($process eq '') { + $process = "NO_PROCESS_NAME"; + } + + $perprocess{$process}->{MM_PAGE_ALLOC} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC}; + $perprocess{$process}->{MM_PAGE_ALLOC_ZONE_LOCKED} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_ZONE_LOCKED}; + $perprocess{$process}->{MM_PAGE_FREE} += $perprocesspid{$process_pid}->{MM_PAGE_FREE}; + $perprocess{$process}->{MM_PAGE_FREE_BATCHED} += $perprocesspid{$process_pid}->{MM_PAGE_FREE_BATCHED}; + $perprocess{$process}->{MM_PAGE_PCPU_DRAIN} += $perprocesspid{$process_pid}->{MM_PAGE_PCPU_DRAIN}; + $perprocess{$process}->{HIGH_PCPU_DRAINS} += $perprocesspid{$process_pid}->{HIGH_PCPU_DRAINS}; + $perprocess{$process}->{HIGH_PCPU_REFILLS} += $perprocesspid{$process_pid}->{HIGH_PCPU_REFILLS}; + $perprocess{$process}->{MM_PAGE_ALLOC_EXTFRAG} += $perprocesspid{$process_pid}->{MM_PAGE_ALLOC_EXTFRAG}; + $perprocess{$process}->{HIGH_EXT_FRAG} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAG}; + $perprocess{$process}->{HIGH_EXT_FRAGMENT_CHANGED} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_CHANGED}; + $perprocess{$process}->{HIGH_EXT_FRAGMENT_SEVERE} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_SEVERE}; + $perprocess{$process}->{HIGH_EXT_FRAGMENT_MODERATE} += $perprocesspid{$process_pid}->{HIGH_EXT_FRAGMENT_MODERATE}; + $perprocess{$process}->{EVENT_UNKNOWN} += $perprocesspid{$process_pid}->{EVENT_UNKNOWN}; + } +} + +sub report() { + if (!$opt_ignorepid) { + dump_stats(\%perprocesspid); + } else { + aggregate_perprocesspid(); + dump_stats(\%perprocess); + } +} + +# Process events or signals until neither is available +sub signal_loop() { + my $sigint_processed; + do { + $sigint_processed = 0; + process_events(); + + # Handle pending signals if any + if ($sigint_pending) { + my $current_time = time; + + if ($sigint_exit) { + print "Received exit signal\n"; + $sigint_pending = 0; + } + if ($sigint_report) { + if ($current_time >= $sigint_received + 2) { + report(); + $sigint_report = 0; + $sigint_pending = 0; + $sigint_processed = 1; + } + } + } + } while ($sigint_pending || $sigint_processed); +} + +signal_loop(); +report(); diff --git a/Documentation/trace/postprocess/trace-vmscan-postprocess.pl b/Documentation/trace/postprocess/trace-vmscan-postprocess.pl new file mode 100644 index 000000000..9efcf5ed8 --- /dev/null +++ b/Documentation/trace/postprocess/trace-vmscan-postprocess.pl @@ -0,0 +1,757 @@ +#!/usr/bin/env perl +# This is a POC for reading the text representation of trace output related to +# page reclaim. It makes an attempt to extract some high-level information on +# what is going on. The accuracy of the parser may vary +# +# Example usage: trace-vmscan-postprocess.pl < /sys/kernel/debug/tracing/trace_pipe +# other options +# --read-procstat If the trace lacks process info, get it from /proc +# --ignore-pid Aggregate processes of the same name together +# +# Copyright (c) IBM Corporation 2009 +# Author: Mel Gorman <mel@csn.ul.ie> +use strict; +use Getopt::Long; + +# Tracepoint events +use constant MM_VMSCAN_DIRECT_RECLAIM_BEGIN => 1; +use constant MM_VMSCAN_DIRECT_RECLAIM_END => 2; +use constant MM_VMSCAN_KSWAPD_WAKE => 3; +use constant MM_VMSCAN_KSWAPD_SLEEP => 4; +use constant MM_VMSCAN_LRU_SHRINK_ACTIVE => 5; +use constant MM_VMSCAN_LRU_SHRINK_INACTIVE => 6; +use constant MM_VMSCAN_LRU_ISOLATE => 7; +use constant MM_VMSCAN_WRITEPAGE_FILE_SYNC => 8; +use constant MM_VMSCAN_WRITEPAGE_ANON_SYNC => 9; +use constant MM_VMSCAN_WRITEPAGE_FILE_ASYNC => 10; +use constant MM_VMSCAN_WRITEPAGE_ANON_ASYNC => 11; +use constant MM_VMSCAN_WRITEPAGE_ASYNC => 12; +use constant EVENT_UNKNOWN => 13; + +# Per-order events +use constant MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER => 11; +use constant MM_VMSCAN_WAKEUP_KSWAPD_PERORDER => 12; +use constant MM_VMSCAN_KSWAPD_WAKE_PERORDER => 13; +use constant HIGH_KSWAPD_REWAKEUP_PERORDER => 14; + +# Constants used to track state +use constant STATE_DIRECT_BEGIN => 15; +use constant STATE_DIRECT_ORDER => 16; +use constant STATE_KSWAPD_BEGIN => 17; +use constant STATE_KSWAPD_ORDER => 18; + +# High-level events extrapolated from tracepoints +use constant HIGH_DIRECT_RECLAIM_LATENCY => 19; +use constant HIGH_KSWAPD_LATENCY => 20; +use constant HIGH_KSWAPD_REWAKEUP => 21; +use constant HIGH_NR_SCANNED => 22; +use constant HIGH_NR_TAKEN => 23; +use constant HIGH_NR_RECLAIMED => 24; +use constant HIGH_NR_FILE_SCANNED => 25; +use constant HIGH_NR_ANON_SCANNED => 26; +use constant HIGH_NR_FILE_RECLAIMED => 27; +use constant HIGH_NR_ANON_RECLAIMED => 28; + +my %perprocesspid; +my %perprocess; +my %last_procmap; +my $opt_ignorepid; +my $opt_read_procstat; + +my $total_wakeup_kswapd; +my ($total_direct_reclaim, $total_direct_nr_scanned); +my ($total_direct_nr_file_scanned, $total_direct_nr_anon_scanned); +my ($total_direct_latency, $total_kswapd_latency); +my ($total_direct_nr_reclaimed); +my ($total_direct_nr_file_reclaimed, $total_direct_nr_anon_reclaimed); +my ($total_direct_writepage_file_sync, $total_direct_writepage_file_async); +my ($total_direct_writepage_anon_sync, $total_direct_writepage_anon_async); +my ($total_kswapd_nr_scanned, $total_kswapd_wake); +my ($total_kswapd_nr_file_scanned, $total_kswapd_nr_anon_scanned); +my ($total_kswapd_writepage_file_sync, $total_kswapd_writepage_file_async); +my ($total_kswapd_writepage_anon_sync, $total_kswapd_writepage_anon_async); +my ($total_kswapd_nr_reclaimed); +my ($total_kswapd_nr_file_reclaimed, $total_kswapd_nr_anon_reclaimed); + +# Catch sigint and exit on request +my $sigint_report = 0; +my $sigint_exit = 0; +my $sigint_pending = 0; +my $sigint_received = 0; +sub sigint_handler { + my $current_time = time; + if ($current_time - 2 > $sigint_received) { + print "SIGINT received, report pending. Hit ctrl-c again to exit\n"; + $sigint_report = 1; + } else { + if (!$sigint_exit) { + print "Second SIGINT received quickly, exiting\n"; + } + $sigint_exit++; + } + + if ($sigint_exit > 3) { + print "Many SIGINTs received, exiting now without report\n"; + exit; + } + + $sigint_received = $current_time; + $sigint_pending = 1; +} +$SIG{INT} = "sigint_handler"; + +# Parse command line options +GetOptions( + 'ignore-pid' => \$opt_ignorepid, + 'read-procstat' => \$opt_read_procstat, +); + +# Defaults for dynamically discovered regex's +my $regex_direct_begin_default = 'order=([0-9]*) may_writepage=([0-9]*) gfp_flags=([A-Z_|]*)'; +my $regex_direct_end_default = 'nr_reclaimed=([0-9]*)'; +my $regex_kswapd_wake_default = 'nid=([0-9]*) order=([0-9]*)'; +my $regex_kswapd_sleep_default = 'nid=([0-9]*)'; +my $regex_wakeup_kswapd_default = 'nid=([0-9]*) zid=([0-9]*) order=([0-9]*) gfp_flags=([A-Z_|]*)'; +my $regex_lru_isolate_default = 'isolate_mode=([0-9]*) classzone_idx=([0-9]*) order=([0-9]*) nr_requested=([0-9]*) nr_scanned=([0-9]*) nr_skipped=([0-9]*) nr_taken=([0-9]*) lru=([a-z_]*)'; +my $regex_lru_shrink_inactive_default = 'nid=([0-9]*) nr_scanned=([0-9]*) nr_reclaimed=([0-9]*) nr_dirty=([0-9]*) nr_writeback=([0-9]*) nr_congested=([0-9]*) nr_immediate=([0-9]*) nr_activate=([0-9]*) nr_ref_keep=([0-9]*) nr_unmap_fail=([0-9]*) priority=([0-9]*) flags=([A-Z_|]*)'; +my $regex_lru_shrink_active_default = 'lru=([A-Z_]*) nr_scanned=([0-9]*) nr_rotated=([0-9]*) priority=([0-9]*)'; +my $regex_writepage_default = 'page=([0-9a-f]*) pfn=([0-9]*) flags=([A-Z_|]*)'; + +# Dyanically discovered regex +my $regex_direct_begin; +my $regex_direct_end; +my $regex_kswapd_wake; +my $regex_kswapd_sleep; +my $regex_wakeup_kswapd; +my $regex_lru_isolate; +my $regex_lru_shrink_inactive; +my $regex_lru_shrink_active; +my $regex_writepage; + +# Static regex used. Specified like this for readability and for use with /o +# (process_pid) (cpus ) ( time ) (tpoint ) (details) +my $regex_traceevent = '\s*([a-zA-Z0-9-]*)\s*(\[[0-9]*\])(\s*[dX.][Nnp.][Hhs.][0-9a-fA-F.]*|)\s*([0-9.]*):\s*([a-zA-Z_]*):\s*(.*)'; +my $regex_statname = '[-0-9]*\s\((.*)\).*'; +my $regex_statppid = '[-0-9]*\s\(.*\)\s[A-Za-z]\s([0-9]*).*'; + +sub generate_traceevent_regex { + my $event = shift; + my $default = shift; + my $regex; + + # Read the event format or use the default + if (!open (FORMAT, "/sys/kernel/debug/tracing/events/$event/format")) { + print("WARNING: Event $event format string not found\n"); + return $default; + } else { + my $line; + while (!eof(FORMAT)) { + $line = <FORMAT>; + $line =~ s/, REC->.*//; + if ($line =~ /^print fmt:\s"(.*)".*/) { + $regex = $1; + $regex =~ s/%s/\([0-9a-zA-Z|_]*\)/g; + $regex =~ s/%p/\([0-9a-f]*\)/g; + $regex =~ s/%d/\([-0-9]*\)/g; + $regex =~ s/%ld/\([-0-9]*\)/g; + $regex =~ s/%lu/\([0-9]*\)/g; + } + } + } + + # Can't handle the print_flags stuff but in the context of this + # script, it really doesn't matter + $regex =~ s/\(REC.*\) \? __print_flags.*//; + + # Verify fields are in the right order + my $tuple; + foreach $tuple (split /\s/, $regex) { + my ($key, $value) = split(/=/, $tuple); + my $expected = shift; + if ($key ne $expected) { + print("WARNING: Format not as expected for event $event '$key' != '$expected'\n"); + $regex =~ s/$key=\((.*)\)/$key=$1/; + } + } + + if (defined shift) { + die("Fewer fields than expected in format"); + } + + return $regex; +} + +$regex_direct_begin = generate_traceevent_regex( + "vmscan/mm_vmscan_direct_reclaim_begin", + $regex_direct_begin_default, + "order", "may_writepage", + "gfp_flags"); +$regex_direct_end = generate_traceevent_regex( + "vmscan/mm_vmscan_direct_reclaim_end", + $regex_direct_end_default, + "nr_reclaimed"); +$regex_kswapd_wake = generate_traceevent_regex( + "vmscan/mm_vmscan_kswapd_wake", + $regex_kswapd_wake_default, + "nid", "order"); +$regex_kswapd_sleep = generate_traceevent_regex( + "vmscan/mm_vmscan_kswapd_sleep", + $regex_kswapd_sleep_default, + "nid"); +$regex_wakeup_kswapd = generate_traceevent_regex( + "vmscan/mm_vmscan_wakeup_kswapd", + $regex_wakeup_kswapd_default, + "nid", "zid", "order", "gfp_flags"); +$regex_lru_isolate = generate_traceevent_regex( + "vmscan/mm_vmscan_lru_isolate", + $regex_lru_isolate_default, + "isolate_mode", "classzone_idx", "order", + "nr_requested", "nr_scanned", "nr_skipped", "nr_taken", + "lru"); +$regex_lru_shrink_inactive = generate_traceevent_regex( + "vmscan/mm_vmscan_lru_shrink_inactive", + $regex_lru_shrink_inactive_default, + "nid", "nr_scanned", "nr_reclaimed", "nr_dirty", "nr_writeback", + "nr_congested", "nr_immediate", "nr_activate", "nr_ref_keep", + "nr_unmap_fail", "priority", "flags"); +$regex_lru_shrink_active = generate_traceevent_regex( + "vmscan/mm_vmscan_lru_shrink_active", + $regex_lru_shrink_active_default, + "nid", "zid", + "lru", + "nr_scanned", "nr_rotated", "priority"); +$regex_writepage = generate_traceevent_regex( + "vmscan/mm_vmscan_writepage", + $regex_writepage_default, + "page", "pfn", "flags"); + +sub read_statline($) { + my $pid = $_[0]; + my $statline; + + if (open(STAT, "/proc/$pid/stat")) { + $statline = <STAT>; + close(STAT); + } + + if ($statline eq '') { + $statline = "-1 (UNKNOWN_PROCESS_NAME) R 0"; + } + + return $statline; +} + +sub guess_process_pid($$) { + my $pid = $_[0]; + my $statline = $_[1]; + + if ($pid == 0) { + return "swapper-0"; + } + + if ($statline !~ /$regex_statname/o) { + die("Failed to math stat line for process name :: $statline"); + } + return "$1-$pid"; +} + +# Convert sec.usec timestamp format +sub timestamp_to_ms($) { + my $timestamp = $_[0]; + + my ($sec, $usec) = split (/\./, $timestamp); + return ($sec * 1000) + ($usec / 1000); +} + +sub process_events { + my $traceevent; + my $process_pid; + my $cpus; + my $timestamp; + my $tracepoint; + my $details; + my $statline; + + # Read each line of the event log +EVENT_PROCESS: + while ($traceevent = <STDIN>) { + if ($traceevent =~ /$regex_traceevent/o) { + $process_pid = $1; + $timestamp = $4; + $tracepoint = $5; + + $process_pid =~ /(.*)-([0-9]*)$/; + my $process = $1; + my $pid = $2; + + if ($process eq "") { + $process = $last_procmap{$pid}; + $process_pid = "$process-$pid"; + } + $last_procmap{$pid} = $process; + + if ($opt_read_procstat) { + $statline = read_statline($pid); + if ($opt_read_procstat && $process eq '') { + $process_pid = guess_process_pid($pid, $statline); + } + } + } else { + next; + } + + # Perl Switch() sucks majorly + if ($tracepoint eq "mm_vmscan_direct_reclaim_begin") { + $timestamp = timestamp_to_ms($timestamp); + $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}++; + $perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN} = $timestamp; + + $details = $6; + if ($details !~ /$regex_direct_begin/o) { + print "WARNING: Failed to parse mm_vmscan_direct_reclaim_begin as expected\n"; + print " $details\n"; + print " $regex_direct_begin\n"; + next; + } + my $order = $1; + $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order]++; + $perprocesspid{$process_pid}->{STATE_DIRECT_ORDER} = $order; + } elsif ($tracepoint eq "mm_vmscan_direct_reclaim_end") { + # Count the event itself + my $index = $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_END}; + $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_END}++; + + # Record how long direct reclaim took this time + if (defined $perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN}) { + $timestamp = timestamp_to_ms($timestamp); + my $order = $perprocesspid{$process_pid}->{STATE_DIRECT_ORDER}; + my $latency = ($timestamp - $perprocesspid{$process_pid}->{STATE_DIRECT_BEGIN}); + $perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index] = "$order-$latency"; + } + } elsif ($tracepoint eq "mm_vmscan_kswapd_wake") { + $details = $6; + if ($details !~ /$regex_kswapd_wake/o) { + print "WARNING: Failed to parse mm_vmscan_kswapd_wake as expected\n"; + print " $details\n"; + print " $regex_kswapd_wake\n"; + next; + } + + my $order = $2; + $perprocesspid{$process_pid}->{STATE_KSWAPD_ORDER} = $order; + if (!$perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN}) { + $timestamp = timestamp_to_ms($timestamp); + $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}++; + $perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN} = $timestamp; + $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order]++; + } else { + $perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP}++; + $perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP_PERORDER}[$order]++; + } + } elsif ($tracepoint eq "mm_vmscan_kswapd_sleep") { + + # Count the event itself + my $index = $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_SLEEP}; + $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_SLEEP}++; + + # Record how long kswapd was awake + $timestamp = timestamp_to_ms($timestamp); + my $order = $perprocesspid{$process_pid}->{STATE_KSWAPD_ORDER}; + my $latency = ($timestamp - $perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN}); + $perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index] = "$order-$latency"; + $perprocesspid{$process_pid}->{STATE_KSWAPD_BEGIN} = 0; + } elsif ($tracepoint eq "mm_vmscan_wakeup_kswapd") { + $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}++; + + $details = $6; + if ($details !~ /$regex_wakeup_kswapd/o) { + print "WARNING: Failed to parse mm_vmscan_wakeup_kswapd as expected\n"; + print " $details\n"; + print " $regex_wakeup_kswapd\n"; + next; + } + my $order = $3; + $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order]++; + } elsif ($tracepoint eq "mm_vmscan_lru_isolate") { + $details = $6; + if ($details !~ /$regex_lru_isolate/o) { + print "WARNING: Failed to parse mm_vmscan_lru_isolate as expected\n"; + print " $details\n"; + print " $regex_lru_isolate/o\n"; + next; + } + my $isolate_mode = $1; + my $nr_scanned = $5; + my $file = $8; + + # To closer match vmstat scanning statistics, only count isolate_both + # and isolate_inactive as scanning. isolate_active is rotation + # isolate_inactive == 1 + # isolate_active == 2 + # isolate_both == 3 + if ($isolate_mode != 2) { + $perprocesspid{$process_pid}->{HIGH_NR_SCANNED} += $nr_scanned; + if ($file =~ /_file/) { + $perprocesspid{$process_pid}->{HIGH_NR_FILE_SCANNED} += $nr_scanned; + } else { + $perprocesspid{$process_pid}->{HIGH_NR_ANON_SCANNED} += $nr_scanned; + } + } + } elsif ($tracepoint eq "mm_vmscan_lru_shrink_inactive") { + $details = $6; + if ($details !~ /$regex_lru_shrink_inactive/o) { + print "WARNING: Failed to parse mm_vmscan_lru_shrink_inactive as expected\n"; + print " $details\n"; + print " $regex_lru_shrink_inactive/o\n"; + next; + } + + my $nr_reclaimed = $3; + my $flags = $12; + my $file = 0; + if ($flags =~ /RECLAIM_WB_FILE/) { + $file = 1; + } + $perprocesspid{$process_pid}->{HIGH_NR_RECLAIMED} += $nr_reclaimed; + if ($file) { + $perprocesspid{$process_pid}->{HIGH_NR_FILE_RECLAIMED} += $nr_reclaimed; + } else { + $perprocesspid{$process_pid}->{HIGH_NR_ANON_RECLAIMED} += $nr_reclaimed; + } + } elsif ($tracepoint eq "mm_vmscan_writepage") { + $details = $6; + if ($details !~ /$regex_writepage/o) { + print "WARNING: Failed to parse mm_vmscan_writepage as expected\n"; + print " $details\n"; + print " $regex_writepage\n"; + next; + } + + my $flags = $3; + my $file = 0; + my $sync_io = 0; + if ($flags =~ /RECLAIM_WB_FILE/) { + $file = 1; + } + if ($flags =~ /RECLAIM_WB_SYNC/) { + $sync_io = 1; + } + if ($sync_io) { + if ($file) { + $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC}++; + } else { + $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}++; + } + } else { + if ($file) { + $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC}++; + } else { + $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}++; + } + } + } else { + $perprocesspid{$process_pid}->{EVENT_UNKNOWN}++; + } + + if ($sigint_pending) { + last EVENT_PROCESS; + } + } +} + +sub dump_stats { + my $hashref = shift; + my %stats = %$hashref; + + # Dump per-process stats + my $process_pid; + my $max_strlen = 0; + + # Get the maximum process name + foreach $process_pid (keys %perprocesspid) { + my $len = length($process_pid); + if ($len > $max_strlen) { + $max_strlen = $len; + } + } + $max_strlen += 2; + + # Work out latencies + printf("\n") if !$opt_ignorepid; + printf("Reclaim latencies expressed as order-latency_in_ms\n") if !$opt_ignorepid; + foreach $process_pid (keys %stats) { + + if (!$stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[0] && + !$stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[0]) { + next; + } + + printf "%-" . $max_strlen . "s ", $process_pid if !$opt_ignorepid; + my $index = 0; + while (defined $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index] || + defined $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]) { + + if ($stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) { + printf("%s ", $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) if !$opt_ignorepid; + my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]); + $total_direct_latency += $latency; + } else { + printf("%s ", $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]) if !$opt_ignorepid; + my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_KSWAPD_LATENCY}[$index]); + $total_kswapd_latency += $latency; + } + $index++; + } + print "\n" if !$opt_ignorepid; + } + + # Print out process activity + printf("\n"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s %8s %8s\n", "Process", "Direct", "Wokeup", "Pages", "Pages", "Pages", "Pages", "Time"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s %8s %8s\n", "details", "Rclms", "Kswapd", "Scanned", "Rclmed", "Sync-IO", "ASync-IO", "Stalled"); + foreach $process_pid (keys %stats) { + + if (!$stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}) { + next; + } + + $total_direct_reclaim += $stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}; + $total_wakeup_kswapd += $stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}; + $total_direct_nr_scanned += $stats{$process_pid}->{HIGH_NR_SCANNED}; + $total_direct_nr_file_scanned += $stats{$process_pid}->{HIGH_NR_FILE_SCANNED}; + $total_direct_nr_anon_scanned += $stats{$process_pid}->{HIGH_NR_ANON_SCANNED}; + $total_direct_nr_reclaimed += $stats{$process_pid}->{HIGH_NR_RECLAIMED}; + $total_direct_nr_file_reclaimed += $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED}; + $total_direct_nr_anon_reclaimed += $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED}; + $total_direct_writepage_file_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC}; + $total_direct_writepage_anon_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}; + $total_direct_writepage_file_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC}; + + $total_direct_writepage_anon_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}; + + my $index = 0; + my $this_reclaim_delay = 0; + while (defined $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]) { + my ($dummy, $latency) = split(/-/, $stats{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$index]); + $this_reclaim_delay += $latency; + $index++; + } + + printf("%-" . $max_strlen . "s %8d %10d %8u %8u %8u %8u %8.3f", + $process_pid, + $stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}, + $stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}, + $stats{$process_pid}->{HIGH_NR_SCANNED}, + $stats{$process_pid}->{HIGH_NR_FILE_SCANNED}, + $stats{$process_pid}->{HIGH_NR_ANON_SCANNED}, + $stats{$process_pid}->{HIGH_NR_RECLAIMED}, + $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED}, + $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED}, + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}, + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}, + $this_reclaim_delay / 1000); + + if ($stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}) { + print " "; + for (my $order = 0; $order < 20; $order++) { + my $count = $stats{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order]; + if ($count != 0) { + print "direct-$order=$count "; + } + } + } + if ($stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}) { + print " "; + for (my $order = 0; $order < 20; $order++) { + my $count = $stats{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order]; + if ($count != 0) { + print "wakeup-$order=$count "; + } + } + } + + print "\n"; + } + + # Print out kswapd activity + printf("\n"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s\n", "Kswapd", "Kswapd", "Order", "Pages", "Pages", "Pages", "Pages"); + printf("%-" . $max_strlen . "s %8s %10s %8s %8s %8s %8s\n", "Instance", "Wakeups", "Re-wakeup", "Scanned", "Rclmed", "Sync-IO", "ASync-IO"); + foreach $process_pid (keys %stats) { + + if (!$stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}) { + next; + } + + $total_kswapd_wake += $stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}; + $total_kswapd_nr_scanned += $stats{$process_pid}->{HIGH_NR_SCANNED}; + $total_kswapd_nr_file_scanned += $stats{$process_pid}->{HIGH_NR_FILE_SCANNED}; + $total_kswapd_nr_anon_scanned += $stats{$process_pid}->{HIGH_NR_ANON_SCANNED}; + $total_kswapd_nr_reclaimed += $stats{$process_pid}->{HIGH_NR_RECLAIMED}; + $total_kswapd_nr_file_reclaimed += $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED}; + $total_kswapd_nr_anon_reclaimed += $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED}; + $total_kswapd_writepage_file_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC}; + $total_kswapd_writepage_anon_sync += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}; + $total_kswapd_writepage_file_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC}; + $total_kswapd_writepage_anon_async += $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}; + + printf("%-" . $max_strlen . "s %8d %10d %8u %8u %8i %8u", + $process_pid, + $stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}, + $stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP}, + $stats{$process_pid}->{HIGH_NR_SCANNED}, + $stats{$process_pid}->{HIGH_NR_FILE_SCANNED}, + $stats{$process_pid}->{HIGH_NR_ANON_SCANNED}, + $stats{$process_pid}->{HIGH_NR_RECLAIMED}, + $stats{$process_pid}->{HIGH_NR_FILE_RECLAIMED}, + $stats{$process_pid}->{HIGH_NR_ANON_RECLAIMED}, + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}, + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} + $stats{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}); + + if ($stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}) { + print " "; + for (my $order = 0; $order < 20; $order++) { + my $count = $stats{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order]; + if ($count != 0) { + print "wake-$order=$count "; + } + } + } + if ($stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP}) { + print " "; + for (my $order = 0; $order < 20; $order++) { + my $count = $stats{$process_pid}->{HIGH_KSWAPD_REWAKEUP_PERORDER}[$order]; + if ($count != 0) { + print "rewake-$order=$count "; + } + } + } + printf("\n"); + } + + # Print out summaries + $total_direct_latency /= 1000; + $total_kswapd_latency /= 1000; + print "\nSummary\n"; + print "Direct reclaims: $total_direct_reclaim\n"; + print "Direct reclaim pages scanned: $total_direct_nr_scanned\n"; + print "Direct reclaim file pages scanned: $total_direct_nr_file_scanned\n"; + print "Direct reclaim anon pages scanned: $total_direct_nr_anon_scanned\n"; + print "Direct reclaim pages reclaimed: $total_direct_nr_reclaimed\n"; + print "Direct reclaim file pages reclaimed: $total_direct_nr_file_reclaimed\n"; + print "Direct reclaim anon pages reclaimed: $total_direct_nr_anon_reclaimed\n"; + print "Direct reclaim write file sync I/O: $total_direct_writepage_file_sync\n"; + print "Direct reclaim write anon sync I/O: $total_direct_writepage_anon_sync\n"; + print "Direct reclaim write file async I/O: $total_direct_writepage_file_async\n"; + print "Direct reclaim write anon async I/O: $total_direct_writepage_anon_async\n"; + print "Wake kswapd requests: $total_wakeup_kswapd\n"; + printf "Time stalled direct reclaim: %-1.2f seconds\n", $total_direct_latency; + print "\n"; + print "Kswapd wakeups: $total_kswapd_wake\n"; + print "Kswapd pages scanned: $total_kswapd_nr_scanned\n"; + print "Kswapd file pages scanned: $total_kswapd_nr_file_scanned\n"; + print "Kswapd anon pages scanned: $total_kswapd_nr_anon_scanned\n"; + print "Kswapd pages reclaimed: $total_kswapd_nr_reclaimed\n"; + print "Kswapd file pages reclaimed: $total_kswapd_nr_file_reclaimed\n"; + print "Kswapd anon pages reclaimed: $total_kswapd_nr_anon_reclaimed\n"; + print "Kswapd reclaim write file sync I/O: $total_kswapd_writepage_file_sync\n"; + print "Kswapd reclaim write anon sync I/O: $total_kswapd_writepage_anon_sync\n"; + print "Kswapd reclaim write file async I/O: $total_kswapd_writepage_file_async\n"; + print "Kswapd reclaim write anon async I/O: $total_kswapd_writepage_anon_async\n"; + printf "Time kswapd awake: %-1.2f seconds\n", $total_kswapd_latency; +} + +sub aggregate_perprocesspid() { + my $process_pid; + my $process; + undef %perprocess; + + foreach $process_pid (keys %perprocesspid) { + $process = $process_pid; + $process =~ s/-([0-9])*$//; + if ($process eq '') { + $process = "NO_PROCESS_NAME"; + } + + $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN} += $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN}; + $perprocess{$process}->{MM_VMSCAN_KSWAPD_WAKE} += $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE}; + $perprocess{$process}->{MM_VMSCAN_WAKEUP_KSWAPD} += $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD}; + $perprocess{$process}->{HIGH_KSWAPD_REWAKEUP} += $perprocesspid{$process_pid}->{HIGH_KSWAPD_REWAKEUP}; + $perprocess{$process}->{HIGH_NR_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_SCANNED}; + $perprocess{$process}->{HIGH_NR_FILE_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_FILE_SCANNED}; + $perprocess{$process}->{HIGH_NR_ANON_SCANNED} += $perprocesspid{$process_pid}->{HIGH_NR_ANON_SCANNED}; + $perprocess{$process}->{HIGH_NR_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_RECLAIMED}; + $perprocess{$process}->{HIGH_NR_FILE_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_FILE_RECLAIMED}; + $perprocess{$process}->{HIGH_NR_ANON_RECLAIMED} += $perprocesspid{$process_pid}->{HIGH_NR_ANON_RECLAIMED}; + $perprocess{$process}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_SYNC}; + $perprocess{$process}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_SYNC}; + $perprocess{$process}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_FILE_ASYNC}; + $perprocess{$process}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC} += $perprocesspid{$process_pid}->{MM_VMSCAN_WRITEPAGE_ANON_ASYNC}; + + for (my $order = 0; $order < 20; $order++) { + $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_DIRECT_RECLAIM_BEGIN_PERORDER}[$order]; + $perprocess{$process}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_WAKEUP_KSWAPD_PERORDER}[$order]; + $perprocess{$process}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order] += $perprocesspid{$process_pid}->{MM_VMSCAN_KSWAPD_WAKE_PERORDER}[$order]; + + } + + # Aggregate direct reclaim latencies + my $wr_index = $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END}; + my $rd_index = 0; + while (defined $perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$rd_index]) { + $perprocess{$process}->{HIGH_DIRECT_RECLAIM_LATENCY}[$wr_index] = $perprocesspid{$process_pid}->{HIGH_DIRECT_RECLAIM_LATENCY}[$rd_index]; + $rd_index++; + $wr_index++; + } + $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END} = $wr_index; + + # Aggregate kswapd latencies + my $wr_index = $perprocess{$process}->{MM_VMSCAN_KSWAPD_SLEEP}; + my $rd_index = 0; + while (defined $perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$rd_index]) { + $perprocess{$process}->{HIGH_KSWAPD_LATENCY}[$wr_index] = $perprocesspid{$process_pid}->{HIGH_KSWAPD_LATENCY}[$rd_index]; + $rd_index++; + $wr_index++; + } + $perprocess{$process}->{MM_VMSCAN_DIRECT_RECLAIM_END} = $wr_index; + } +} + +sub report() { + if (!$opt_ignorepid) { + dump_stats(\%perprocesspid); + } else { + aggregate_perprocesspid(); + dump_stats(\%perprocess); + } +} + +# Process events or signals until neither is available +sub signal_loop() { + my $sigint_processed; + do { + $sigint_processed = 0; + process_events(); + + # Handle pending signals if any + if ($sigint_pending) { + my $current_time = time; + + if ($sigint_exit) { + print "Received exit signal\n"; + $sigint_pending = 0; + } + if ($sigint_report) { + if ($current_time >= $sigint_received + 2) { + report(); + $sigint_report = 0; + $sigint_pending = 0; + $sigint_processed = 1; + } + } + } + } while ($sigint_pending || $sigint_processed); +} + +signal_loop(); +report(); diff --git a/Documentation/trace/ring-buffer-design.txt b/Documentation/trace/ring-buffer-design.txt new file mode 100644 index 000000000..ff747b6fa --- /dev/null +++ b/Documentation/trace/ring-buffer-design.txt @@ -0,0 +1,955 @@ + Lockless Ring Buffer Design + =========================== + +Copyright 2009 Red Hat Inc. + Author: Steven Rostedt <srostedt@redhat.com> + License: The GNU Free Documentation License, Version 1.2 + (dual licensed under the GPL v2) +Reviewers: Mathieu Desnoyers, Huang Ying, Hidetoshi Seto, + and Frederic Weisbecker. + + +Written for: 2.6.31 + +Terminology used in this Document +--------------------------------- + +tail - where new writes happen in the ring buffer. + +head - where new reads happen in the ring buffer. + +producer - the task that writes into the ring buffer (same as writer) + +writer - same as producer + +consumer - the task that reads from the buffer (same as reader) + +reader - same as consumer. + +reader_page - A page outside the ring buffer used solely (for the most part) + by the reader. + +head_page - a pointer to the page that the reader will use next + +tail_page - a pointer to the page that will be written to next + +commit_page - a pointer to the page with the last finished non-nested write. + +cmpxchg - hardware-assisted atomic transaction that performs the following: + + A = B iff previous A == C + + R = cmpxchg(A, C, B) is saying that we replace A with B if and only if + current A is equal to C, and we put the old (current) A into R + + R gets the previous A regardless if A is updated with B or not. + + To see if the update was successful a compare of R == C may be used. + +The Generic Ring Buffer +----------------------- + +The ring buffer can be used in either an overwrite mode or in +producer/consumer mode. + +Producer/consumer mode is where if the producer were to fill up the +buffer before the consumer could free up anything, the producer +will stop writing to the buffer. This will lose most recent events. + +Overwrite mode is where if the producer were to fill up the buffer +before the consumer could free up anything, the producer will +overwrite the older data. This will lose the oldest events. + +No two writers can write at the same time (on the same per-cpu buffer), +but a writer may interrupt another writer, but it must finish writing +before the previous writer may continue. This is very important to the +algorithm. The writers act like a "stack". The way interrupts works +enforces this behavior. + + + writer1 start + <preempted> writer2 start + <preempted> writer3 start + writer3 finishes + writer2 finishes + writer1 finishes + +This is very much like a writer being preempted by an interrupt and +the interrupt doing a write as well. + +Readers can happen at any time. But no two readers may run at the +same time, nor can a reader preempt/interrupt another reader. A reader +cannot preempt/interrupt a writer, but it may read/consume from the +buffer at the same time as a writer is writing, but the reader must be +on another processor to do so. A reader may read on its own processor +and can be preempted by a writer. + +A writer can preempt a reader, but a reader cannot preempt a writer. +But a reader can read the buffer at the same time (on another processor) +as a writer. + +The ring buffer is made up of a list of pages held together by a linked list. + +At initialization a reader page is allocated for the reader that is not +part of the ring buffer. + +The head_page, tail_page and commit_page are all initialized to point +to the same page. + +The reader page is initialized to have its next pointer pointing to +the head page, and its previous pointer pointing to a page before +the head page. + +The reader has its own page to use. At start up time, this page is +allocated but is not attached to the list. When the reader wants +to read from the buffer, if its page is empty (like it is on start-up), +it will swap its page with the head_page. The old reader page will +become part of the ring buffer and the head_page will be removed. +The page after the inserted page (old reader_page) will become the +new head page. + +Once the new page is given to the reader, the reader could do what +it wants with it, as long as a writer has left that page. + +A sample of how the reader page is swapped: Note this does not +show the head page in the buffer, it is for demonstrating a swap +only. + + +------+ + |reader| RING BUFFER + |page | + +------+ + +---+ +---+ +---+ + | |-->| |-->| | + | |<--| |<--| | + +---+ +---+ +---+ + ^ | ^ | + | +-------------+ | + +-----------------+ + + + +------+ + |reader| RING BUFFER + |page |-------------------+ + +------+ v + | +---+ +---+ +---+ + | | |-->| |-->| | + | | |<--| |<--| |<-+ + | +---+ +---+ +---+ | + | ^ | ^ | | + | | +-------------+ | | + | +-----------------+ | + +------------------------------------+ + + +------+ + |reader| RING BUFFER + |page |-------------------+ + +------+ <---------------+ v + | ^ +---+ +---+ +---+ + | | | |-->| |-->| | + | | | | | |<--| |<-+ + | | +---+ +---+ +---+ | + | | | ^ | | + | | +-------------+ | | + | +-----------------------------+ | + +------------------------------------+ + + +------+ + |buffer| RING BUFFER + |page |-------------------+ + +------+ <---------------+ v + | ^ +---+ +---+ +---+ + | | | | | |-->| | + | | New | | | |<--| |<-+ + | | Reader +---+ +---+ +---+ | + | | page ----^ | | + | | | | + | +-----------------------------+ | + +------------------------------------+ + + + +It is possible that the page swapped is the commit page and the tail page, +if what is in the ring buffer is less than what is held in a buffer page. + + + reader page commit page tail page + | | | + v | | + +---+ | | + | |<----------+ | + | |<------------------------+ + | |------+ + +---+ | + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +This case is still valid for this algorithm. +When the writer leaves the page, it simply goes into the ring buffer +since the reader page still points to the next location in the ring +buffer. + + +The main pointers: + + reader page - The page used solely by the reader and is not part + of the ring buffer (may be swapped in) + + head page - the next page in the ring buffer that will be swapped + with the reader page. + + tail page - the page where the next write will take place. + + commit page - the page that last finished a write. + +The commit page only is updated by the outermost writer in the +writer stack. A writer that preempts another writer will not move the +commit page. + +When data is written into the ring buffer, a position is reserved +in the ring buffer and passed back to the writer. When the writer +is finished writing data into that position, it commits the write. + +Another write (or a read) may take place at anytime during this +transaction. If another write happens it must finish before continuing +with the previous write. + + + Write reserve: + + Buffer page + +---------+ + |written | + +---------+ <--- given back to writer (current commit) + |reserved | + +---------+ <--- tail pointer + | empty | + +---------+ + + Write commit: + + Buffer page + +---------+ + |written | + +---------+ + |written | + +---------+ <--- next position for write (current commit) + | empty | + +---------+ + + + If a write happens after the first reserve: + + Buffer page + +---------+ + |written | + +---------+ <-- current commit + |reserved | + +---------+ <--- given back to second writer + |reserved | + +---------+ <--- tail pointer + + After second writer commits: + + + Buffer page + +---------+ + |written | + +---------+ <--(last full commit) + |reserved | + +---------+ + |pending | + |commit | + +---------+ <--- tail pointer + + When the first writer commits: + + Buffer page + +---------+ + |written | + +---------+ + |written | + +---------+ + |written | + +---------+ <--(last full commit and tail pointer) + + +The commit pointer points to the last write location that was +committed without preempting another write. When a write that +preempted another write is committed, it only becomes a pending commit +and will not be a full commit until all writes have been committed. + +The commit page points to the page that has the last full commit. +The tail page points to the page with the last write (before +committing). + +The tail page is always equal to or after the commit page. It may +be several pages ahead. If the tail page catches up to the commit +page then no more writes may take place (regardless of the mode +of the ring buffer: overwrite and produce/consumer). + +The order of pages is: + + head page + commit page + tail page + +Possible scenario: + tail page + head page commit page | + | | | + v v v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +There is a special case that the head page is after either the commit page +and possibly the tail page. That is when the commit (and tail) page has been +swapped with the reader page. This is because the head page is always +part of the ring buffer, but the reader page is not. Whenever there +has been less than a full page that has been committed inside the ring buffer, +and a reader swaps out a page, it will be swapping out the commit page. + + + reader page commit page tail page + | | | + v | | + +---+ | | + | |<----------+ | + | |<------------------------+ + | |------+ + +---+ | + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + ^ + | + head page + + +In this case, the head page will not move when the tail and commit +move back into the ring buffer. + +The reader cannot swap a page into the ring buffer if the commit page +is still on that page. If the read meets the last commit (real commit +not pending or reserved), then there is nothing more to read. +The buffer is considered empty until another full commit finishes. + +When the tail meets the head page, if the buffer is in overwrite mode, +the head page will be pushed ahead one. If the buffer is in producer/consumer +mode, the write will fail. + +Overwrite mode: + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + ^ + | + head page + + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + ^ + | + head page + + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + ^ + | + head page + +Note, the reader page will still point to the previous head page. +But when a swap takes place, it will use the most recent head page. + + +Making the Ring Buffer Lockless: +-------------------------------- + +The main idea behind the lockless algorithm is to combine the moving +of the head_page pointer with the swapping of pages with the reader. +State flags are placed inside the pointer to the page. To do this, +each page must be aligned in memory by 4 bytes. This will allow the 2 +least significant bits of the address to be used as flags, since +they will always be zero for the address. To get the address, +simply mask out the flags. + + MASK = ~3 + + address & MASK + +Two flags will be kept by these two bits: + + HEADER - the page being pointed to is a head page + + UPDATE - the page being pointed to is being updated by a writer + and was or is about to be a head page. + + + reader page + | + v + +---+ + | |------+ + +---+ | + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + +The above pointer "-H->" would have the HEADER flag set. That is +the next page is the next page to be swapped out by the reader. +This pointer means the next page is the head page. + +When the tail page meets the head pointer, it will use cmpxchg to +change the pointer to the UPDATE state: + + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +"-U->" represents a pointer in the UPDATE state. + +Any access to the reader will need to take some sort of lock to serialize +the readers. But the writers will never take a lock to write to the +ring buffer. This means we only need to worry about a single reader, +and writes only preempt in "stack" formation. + +When the reader tries to swap the page with the ring buffer, it +will also use cmpxchg. If the flag bit in the pointer to the +head page does not have the HEADER flag set, the compare will fail +and the reader will need to look for the new head page and try again. +Note, the flags UPDATE and HEADER are never set at the same time. + +The reader swaps the reader page as follows: + + +------+ + |reader| RING BUFFER + |page | + +------+ + +---+ +---+ +---+ + | |--->| |--->| | + | |<---| |<---| | + +---+ +---+ +---+ + ^ | ^ | + | +---------------+ | + +-----H-------------+ + +The reader sets the reader page next pointer as HEADER to the page after +the head page. + + + +------+ + |reader| RING BUFFER + |page |-------H-----------+ + +------+ v + | +---+ +---+ +---+ + | | |--->| |--->| | + | | |<---| |<---| |<-+ + | +---+ +---+ +---+ | + | ^ | ^ | | + | | +---------------+ | | + | +-----H-------------+ | + +--------------------------------------+ + +It does a cmpxchg with the pointer to the previous head page to make it +point to the reader page. Note that the new pointer does not have the HEADER +flag set. This action atomically moves the head page forward. + + +------+ + |reader| RING BUFFER + |page |-------H-----------+ + +------+ v + | ^ +---+ +---+ +---+ + | | | |-->| |-->| | + | | | |<--| |<--| |<-+ + | | +---+ +---+ +---+ | + | | | ^ | | + | | +-------------+ | | + | +-----------------------------+ | + +------------------------------------+ + +After the new head page is set, the previous pointer of the head page is +updated to the reader page. + + +------+ + |reader| RING BUFFER + |page |-------H-----------+ + +------+ <---------------+ v + | ^ +---+ +---+ +---+ + | | | |-->| |-->| | + | | | | | |<--| |<-+ + | | +---+ +---+ +---+ | + | | | ^ | | + | | +-------------+ | | + | +-----------------------------+ | + +------------------------------------+ + + +------+ + |buffer| RING BUFFER + |page |-------H-----------+ <--- New head page + +------+ <---------------+ v + | ^ +---+ +---+ +---+ + | | | | | |-->| | + | | New | | | |<--| |<-+ + | | Reader +---+ +---+ +---+ | + | | page ----^ | | + | | | | + | +-----------------------------+ | + +------------------------------------+ + +Another important point: The page that the reader page points back to +by its previous pointer (the one that now points to the new head page) +never points back to the reader page. That is because the reader page is +not part of the ring buffer. Traversing the ring buffer via the next pointers +will always stay in the ring buffer. Traversing the ring buffer via the +prev pointers may not. + +Note, the way to determine a reader page is simply by examining the previous +pointer of the page. If the next pointer of the previous page does not +point back to the original page, then the original page is a reader page: + + + +--------+ + | reader | next +----+ + | page |-------->| |<====== (buffer page) + +--------+ +----+ + | | ^ + | v | next + prev | +----+ + +------------->| | + +----+ + +The way the head page moves forward: + +When the tail page meets the head page and the buffer is in overwrite mode +and more writes take place, the head page must be moved forward before the +writer may move the tail page. The way this is done is that the writer +performs a cmpxchg to convert the pointer to the head page from the HEADER +flag to have the UPDATE flag set. Once this is done, the reader will +not be able to swap the head page from the buffer, nor will it be able to +move the head page, until the writer is finished with the move. + +This eliminates any races that the reader can have on the writer. The reader +must spin, and this is why the reader cannot preempt the writer. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The following page will be made into the new head page. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +After the new head page has been set, we can set the old head page +pointer back to NORMAL. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +After the head page has been moved, the tail page may now move forward. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + +The above are the trivial updates. Now for the more complex scenarios. + + +As stated before, if enough writes preempt the first write, the +tail page may make it all the way around the buffer and meet the commit +page. At this time, we must start dropping writes (usually with some kind +of warning to the user). But what happens if the commit was still on the +reader page? The commit page is not part of the ring buffer. The tail page +must account for this. + + + reader page commit page + | | + v | + +---+ | + | |<----------+ + | | + | |------+ + +---+ | + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + ^ + | + tail page + +If the tail page were to simply push the head page forward, the commit when +leaving the reader page would not be pointing to the correct page. + +The solution to this is to test if the commit page is on the reader page +before pushing the head page. If it is, then it can be assumed that the +tail page wrapped the buffer, and we must drop new writes. + +This is not a race condition, because the commit page can only be moved +by the outermost writer (the writer that was preempted). +This means that the commit will not move while a writer is moving the +tail page. The reader cannot swap the reader page if it is also being +used as the commit page. The reader can simply check that the commit +is off the reader page. Once the commit page leaves the reader page +it will never go back on it unless a reader does another swap with the +buffer page that is also the commit page. + + +Nested writes +------------- + +In the pushing forward of the tail page we must first push forward +the head page if the head page is the next page. If the head page +is not the next page, the tail page is simply updated with a cmpxchg. + +Only writers move the tail page. This must be done atomically to protect +against nested writers. + + temp_page = tail_page + next_page = temp_page->next + cmpxchg(tail_page, temp_page, next_page) + +The above will update the tail page if it is still pointing to the expected +page. If this fails, a nested write pushed it forward, the current write +does not need to push it. + + + temp page + | + v + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +Nested write comes in and moves the tail page forward: + + tail page (moved by nested writer) + temp page | + | | + v v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The above would fail the cmpxchg, but since the tail page has already +been moved forward, the writer will just try again to reserve storage +on the new tail page. + +But the moving of the head page is a bit more complex. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The write converts the head page pointer to UPDATE. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +But if a nested writer preempts here, it will see that the next +page is a head page, but it is also nested. It will detect that +it is nested and will save that information. The detection is the +fact that it sees the UPDATE flag instead of a HEADER or NORMAL +pointer. + +The nested writer will set the new head page pointer. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +But it will not reset the update back to normal. Only the writer +that converted a pointer from HEAD to UPDATE will convert it back +to NORMAL. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +After the nested writer finishes, the outermost writer will convert +the UPDATE pointer to NORMAL. + + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + +It can be even more complex if several nested writes came in and moved +the tail page ahead several pages: + + +(first writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-H->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The write converts the head page pointer to UPDATE. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +Next writer comes in, and sees the update and sets up the new +head page. + +(second writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The nested writer moves the tail page forward. But does not set the old +update page to NORMAL because it is not the outermost writer. + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +Another writer preempts and sees the page after the tail page is a head page. +It changes it from HEAD to UPDATE. + +(third writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-U->| |---> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The writer will move the head page forward: + + +(third writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-U->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +But now that the third writer did change the HEAD flag to UPDATE it +will convert it to normal: + + +(third writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + +Then it will move the tail page, and return back to the second writer. + + +(second writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + + +The second writer will fail to move the tail page because it was already +moved, so it will try again and add its data to the new tail page. +It will return to the first writer. + + +(first writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +The first writer cannot know atomically if the tail page moved +while it updates the HEAD page. It will then update the head page to +what it thinks is the new head page. + + +(first writer) + + tail page + | + v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +Since the cmpxchg returns the old value of the pointer the first writer +will see it succeeded in updating the pointer from NORMAL to HEAD. +But as we can see, this is not good enough. It must also check to see +if the tail page is either where it use to be or on the next page: + + +(first writer) + + A B tail page + | | | + v v v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |-H->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +If tail page != A and tail page != B, then it must reset the pointer +back to NORMAL. The fact that it only needs to worry about nested +writers means that it only needs to check this after setting the HEAD page. + + +(first writer) + + A B tail page + | | | + v v v + +---+ +---+ +---+ +---+ +<---| |--->| |-U->| |--->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + +Now the writer can update the head page. This is also why the head page must +remain in UPDATE and only reset by the outermost writer. This prevents +the reader from seeing the incorrect head page. + + +(first writer) + + A B tail page + | | | + v v v + +---+ +---+ +---+ +---+ +<---| |--->| |--->| |--->| |-H-> +--->| |<---| |<---| |<---| |<--- + +---+ +---+ +---+ +---+ + diff --git a/Documentation/trace/stm.rst b/Documentation/trace/stm.rst new file mode 100644 index 000000000..2c22ddb7f --- /dev/null +++ b/Documentation/trace/stm.rst @@ -0,0 +1,123 @@ +=================== +System Trace Module +=================== + +System Trace Module (STM) is a device described in MIPI STP specs as +STP trace stream generator. STP (System Trace Protocol) is a trace +protocol multiplexing data from multiple trace sources, each one of +which is assigned a unique pair of master and channel. While some of +these masters and channels are statically allocated to certain +hardware trace sources, others are available to software. Software +trace sources are usually free to pick for themselves any +master/channel combination from this pool. + +On the receiving end of this STP stream (the decoder side), trace +sources can only be identified by master/channel combination, so in +order for the decoder to be able to make sense of the trace that +involves multiple trace sources, it needs to be able to map those +master/channel pairs to the trace sources that it understands. + +For instance, it is helpful to know that syslog messages come on +master 7 channel 15, while arbitrary user applications can use masters +48 to 63 and channels 0 to 127. + +To solve this mapping problem, stm class provides a policy management +mechanism via configfs, that allows defining rules that map string +identifiers to ranges of masters and channels. If these rules (policy) +are consistent with what decoder expects, it will be able to properly +process the trace data. + +This policy is a tree structure containing rules (policy_node) that +have a name (string identifier) and a range of masters and channels +associated with it, located in "stp-policy" subsystem directory in +configfs. The topmost directory's name (the policy) is formatted as +the STM device name to which this policy applies and and arbitrary +string identifier separated by a stop. From the examle above, a rule +may look like this:: + + $ ls /config/stp-policy/dummy_stm.my-policy/user + channels masters + $ cat /config/stp-policy/dummy_stm.my-policy/user/masters + 48 63 + $ cat /config/stp-policy/dummy_stm.my-policy/user/channels + 0 127 + +which means that the master allocation pool for this rule consists of +masters 48 through 63 and channel allocation pool has channels 0 +through 127 in it. Now, any producer (trace source) identifying itself +with "user" identification string will be allocated a master and +channel from within these ranges. + +These rules can be nested, for example, one can define a rule "dummy" +under "user" directory from the example above and this new rule will +be used for trace sources with the id string of "user/dummy". + +Trace sources have to open the stm class device's node and write their +trace data into its file descriptor. In order to identify themselves +to the policy, they need to do a STP_POLICY_ID_SET ioctl on this file +descriptor providing their id string. Otherwise, they will be +automatically allocated a master/channel pair upon first write to this +file descriptor according to the "default" rule of the policy, if such +exists. + +Some STM devices may allow direct mapping of the channel mmio regions +to userspace for zero-copy writing. One mappable page (in terms of +mmu) will usually contain multiple channels' mmios, so the user will +need to allocate that many channels to themselves (via the +aforementioned ioctl() call) to be able to do this. That is, if your +stm device's channel mmio region is 64 bytes and hardware page size is +4096 bytes, after a successful STP_POLICY_ID_SET ioctl() call with +width==64, you should be able to mmap() one page on this file +descriptor and obtain direct access to an mmio region for 64 channels. + +Examples of STM devices are Intel(R) Trace Hub [1] and Coresight STM +[2]. + +stm_source +========== + +For kernel-based trace sources, there is "stm_source" device +class. Devices of this class can be connected and disconnected to/from +stm devices at runtime via a sysfs attribute called "stm_source_link" +by writing the name of the desired stm device there, for example:: + + $ echo dummy_stm.0 > /sys/class/stm_source/console/stm_source_link + +For examples on how to use stm_source interface in the kernel, refer +to stm_console, stm_heartbeat or stm_ftrace drivers. + +Each stm_source device will need to assume a master and a range of +channels, depending on how many channels it requires. These are +allocated for the device according to the policy configuration. If +there's a node in the root of the policy directory that matches the +stm_source device's name (for example, "console"), this node will be +used to allocate master and channel numbers. If there's no such policy +node, the stm core will pick the first contiguous chunk of channels +within the first available master. Note that the node must exist +before the stm_source device is connected to its stm device. + +stm_console +=========== + +One implementation of this interface also used in the example above is +the "stm_console" driver, which basically provides a one-way console +for kernel messages over an stm device. + +To configure the master/channel pair that will be assigned to this +console in the STP stream, create a "console" policy entry (see the +beginning of this text on how to do that). When initialized, it will +consume one channel. + +stm_ftrace +========== + +This is another "stm_source" device, once the stm_ftrace has been +linked with an stm device, and if "function" tracer is enabled, +function address and parent function address which Ftrace subsystem +would store into ring buffer will be exported via the stm device at +the same time. + +Currently only Ftrace "function" tracer is supported. + +* [1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf +* [2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html diff --git a/Documentation/trace/tracepoint-analysis.rst b/Documentation/trace/tracepoint-analysis.rst new file mode 100644 index 000000000..716326b9f --- /dev/null +++ b/Documentation/trace/tracepoint-analysis.rst @@ -0,0 +1,338 @@ +========================================================= +Notes on Analysing Behaviour Using Events and Tracepoints +========================================================= +:Author: Mel Gorman (PCL information heavily based on email from Ingo Molnar) + +1. Introduction +=============== + +Tracepoints (see Documentation/trace/tracepoints.rst) can be used without +creating custom kernel modules to register probe functions using the event +tracing infrastructure. + +Simplistically, tracepoints represent important events that can be +taken in conjunction with other tracepoints to build a "Big Picture" of +what is going on within the system. There are a large number of methods for +gathering and interpreting these events. Lacking any current Best Practises, +this document describes some of the methods that can be used. + +This document assumes that debugfs is mounted on /sys/kernel/debug and that +the appropriate tracing options have been configured into the kernel. It is +assumed that the PCL tool tools/perf has been installed and is in your path. + +2. Listing Available Events +=========================== + +2.1 Standard Utilities +---------------------- + +All possible events are visible from /sys/kernel/debug/tracing/events. Simply +calling:: + + $ find /sys/kernel/debug/tracing/events -type d + +will give a fair indication of the number of events available. + +2.2 PCL (Performance Counters for Linux) +---------------------------------------- + +Discovery and enumeration of all counters and events, including tracepoints, +are available with the perf tool. Getting a list of available events is a +simple case of:: + + $ perf list 2>&1 | grep Tracepoint + ext4:ext4_free_inode [Tracepoint event] + ext4:ext4_request_inode [Tracepoint event] + ext4:ext4_allocate_inode [Tracepoint event] + ext4:ext4_write_begin [Tracepoint event] + ext4:ext4_ordered_write_end [Tracepoint event] + [ .... remaining output snipped .... ] + + +3. Enabling Events +================== + +3.1 System-Wide Event Enabling +------------------------------ + +See Documentation/trace/events.rst for a proper description on how events +can be enabled system-wide. A short example of enabling all events related +to page allocation would look something like:: + + $ for i in `find /sys/kernel/debug/tracing/events -name "enable" | grep mm_`; do echo 1 > $i; done + +3.2 System-Wide Event Enabling with SystemTap +--------------------------------------------- + +In SystemTap, tracepoints are accessible using the kernel.trace() function +call. The following is an example that reports every 5 seconds what processes +were allocating the pages. +:: + + global page_allocs + + probe kernel.trace("mm_page_alloc") { + page_allocs[execname()]++ + } + + function print_count() { + printf ("%-25s %-s\n", "#Pages Allocated", "Process Name") + foreach (proc in page_allocs-) + printf("%-25d %s\n", page_allocs[proc], proc) + printf ("\n") + delete page_allocs + } + + probe timer.s(5) { + print_count() + } + +3.3 System-Wide Event Enabling with PCL +--------------------------------------- + +By specifying the -a switch and analysing sleep, the system-wide events +for a duration of time can be examined. +:: + + $ perf stat -a \ + -e kmem:mm_page_alloc -e kmem:mm_page_free \ + -e kmem:mm_page_free_batched \ + sleep 10 + Performance counter stats for 'sleep 10': + + 9630 kmem:mm_page_alloc + 2143 kmem:mm_page_free + 7424 kmem:mm_page_free_batched + + 10.002577764 seconds time elapsed + +Similarly, one could execute a shell and exit it as desired to get a report +at that point. + +3.4 Local Event Enabling +------------------------ + +Documentation/trace/ftrace.rst describes how to enable events on a per-thread +basis using set_ftrace_pid. + +3.5 Local Event Enablement with PCL +----------------------------------- + +Events can be activated and tracked for the duration of a process on a local +basis using PCL such as follows. +:: + + $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \ + -e kmem:mm_page_free_batched ./hackbench 10 + Time: 0.909 + + Performance counter stats for './hackbench 10': + + 17803 kmem:mm_page_alloc + 12398 kmem:mm_page_free + 4827 kmem:mm_page_free_batched + + 0.973913387 seconds time elapsed + +4. Event Filtering +================== + +Documentation/trace/ftrace.rst covers in-depth how to filter events in +ftrace. Obviously using grep and awk of trace_pipe is an option as well +as any script reading trace_pipe. + +5. Analysing Event Variances with PCL +===================================== + +Any workload can exhibit variances between runs and it can be important +to know what the standard deviation is. By and large, this is left to the +performance analyst to do it by hand. In the event that the discrete event +occurrences are useful to the performance analyst, then perf can be used. +:: + + $ perf stat --repeat 5 -e kmem:mm_page_alloc -e kmem:mm_page_free + -e kmem:mm_page_free_batched ./hackbench 10 + Time: 0.890 + Time: 0.895 + Time: 0.915 + Time: 1.001 + Time: 0.899 + + Performance counter stats for './hackbench 10' (5 runs): + + 16630 kmem:mm_page_alloc ( +- 3.542% ) + 11486 kmem:mm_page_free ( +- 4.771% ) + 4730 kmem:mm_page_free_batched ( +- 2.325% ) + + 0.982653002 seconds time elapsed ( +- 1.448% ) + +In the event that some higher-level event is required that depends on some +aggregation of discrete events, then a script would need to be developed. + +Using --repeat, it is also possible to view how events are fluctuating over +time on a system-wide basis using -a and sleep. +:: + + $ perf stat -e kmem:mm_page_alloc -e kmem:mm_page_free \ + -e kmem:mm_page_free_batched \ + -a --repeat 10 \ + sleep 1 + Performance counter stats for 'sleep 1' (10 runs): + + 1066 kmem:mm_page_alloc ( +- 26.148% ) + 182 kmem:mm_page_free ( +- 5.464% ) + 890 kmem:mm_page_free_batched ( +- 30.079% ) + + 1.002251757 seconds time elapsed ( +- 0.005% ) + +6. Higher-Level Analysis with Helper Scripts +============================================ + +When events are enabled the events that are triggering can be read from +/sys/kernel/debug/tracing/trace_pipe in human-readable format although binary +options exist as well. By post-processing the output, further information can +be gathered on-line as appropriate. Examples of post-processing might include + + - Reading information from /proc for the PID that triggered the event + - Deriving a higher-level event from a series of lower-level events. + - Calculating latencies between two events + +Documentation/trace/postprocess/trace-pagealloc-postprocess.pl is an example +script that can read trace_pipe from STDIN or a copy of a trace. When used +on-line, it can be interrupted once to generate a report without exiting +and twice to exit. + +Simplistically, the script just reads STDIN and counts up events but it +also can do more such as + + - Derive high-level events from many low-level events. If a number of pages + are freed to the main allocator from the per-CPU lists, it recognises + that as one per-CPU drain even though there is no specific tracepoint + for that event + - It can aggregate based on PID or individual process number + - In the event memory is getting externally fragmented, it reports + on whether the fragmentation event was severe or moderate. + - When receiving an event about a PID, it can record who the parent was so + that if large numbers of events are coming from very short-lived + processes, the parent process responsible for creating all the helpers + can be identified + +7. Lower-Level Analysis with PCL +================================ + +There may also be a requirement to identify what functions within a program +were generating events within the kernel. To begin this sort of analysis, the +data must be recorded. At the time of writing, this required root: +:: + + $ perf record -c 1 \ + -e kmem:mm_page_alloc -e kmem:mm_page_free \ + -e kmem:mm_page_free_batched \ + ./hackbench 10 + Time: 0.894 + [ perf record: Captured and wrote 0.733 MB perf.data (~32010 samples) ] + +Note the use of '-c 1' to set the event period to sample. The default sample +period is quite high to minimise overhead but the information collected can be +very coarse as a result. + +This record outputted a file called perf.data which can be analysed using +perf report. +:: + + $ perf report + # Samples: 30922 + # + # Overhead Command Shared Object + # ........ ......... ................................ + # + 87.27% hackbench [vdso] + 6.85% hackbench /lib/i686/cmov/libc-2.9.so + 2.62% hackbench /lib/ld-2.9.so + 1.52% perf [vdso] + 1.22% hackbench ./hackbench + 0.48% hackbench [kernel] + 0.02% perf /lib/i686/cmov/libc-2.9.so + 0.01% perf /usr/bin/perf + 0.01% perf /lib/ld-2.9.so + 0.00% hackbench /lib/i686/cmov/libpthread-2.9.so + # + # (For more details, try: perf report --sort comm,dso,symbol) + # + +According to this, the vast majority of events triggered on events +within the VDSO. With simple binaries, this will often be the case so let's +take a slightly different example. In the course of writing this, it was +noticed that X was generating an insane amount of page allocations so let's look +at it: +:: + + $ perf record -c 1 -f \ + -e kmem:mm_page_alloc -e kmem:mm_page_free \ + -e kmem:mm_page_free_batched \ + -p `pidof X` + +This was interrupted after a few seconds and +:: + + $ perf report + # Samples: 27666 + # + # Overhead Command Shared Object + # ........ ....... ....................................... + # + 51.95% Xorg [vdso] + 47.95% Xorg /opt/gfx-test/lib/libpixman-1.so.0.13.1 + 0.09% Xorg /lib/i686/cmov/libc-2.9.so + 0.01% Xorg [kernel] + # + # (For more details, try: perf report --sort comm,dso,symbol) + # + +So, almost half of the events are occurring in a library. To get an idea which +symbol: +:: + + $ perf report --sort comm,dso,symbol + # Samples: 27666 + # + # Overhead Command Shared Object Symbol + # ........ ....... ....................................... ...... + # + 51.95% Xorg [vdso] [.] 0x000000ffffe424 + 47.93% Xorg /opt/gfx-test/lib/libpixman-1.so.0.13.1 [.] pixmanFillsse2 + 0.09% Xorg /lib/i686/cmov/libc-2.9.so [.] _int_malloc + 0.01% Xorg /opt/gfx-test/lib/libpixman-1.so.0.13.1 [.] pixman_region32_copy_f + 0.01% Xorg [kernel] [k] read_hpet + 0.01% Xorg /opt/gfx-test/lib/libpixman-1.so.0.13.1 [.] get_fast_path + 0.00% Xorg [kernel] [k] ftrace_trace_userstack + +To see where within the function pixmanFillsse2 things are going wrong: +:: + + $ perf annotate pixmanFillsse2 + [ ... ] + 0.00 : 34eeb: 0f 18 08 prefetcht0 (%eax) + : } + : + : extern __inline void __attribute__((__gnu_inline__, __always_inline__, _ + : _mm_store_si128 (__m128i *__P, __m128i __B) : { + : *__P = __B; + 12.40 : 34eee: 66 0f 7f 80 40 ff ff movdqa %xmm0,-0xc0(%eax) + 0.00 : 34ef5: ff + 12.40 : 34ef6: 66 0f 7f 80 50 ff ff movdqa %xmm0,-0xb0(%eax) + 0.00 : 34efd: ff + 12.39 : 34efe: 66 0f 7f 80 60 ff ff movdqa %xmm0,-0xa0(%eax) + 0.00 : 34f05: ff + 12.67 : 34f06: 66 0f 7f 80 70 ff ff movdqa %xmm0,-0x90(%eax) + 0.00 : 34f0d: ff + 12.58 : 34f0e: 66 0f 7f 40 80 movdqa %xmm0,-0x80(%eax) + 12.31 : 34f13: 66 0f 7f 40 90 movdqa %xmm0,-0x70(%eax) + 12.40 : 34f18: 66 0f 7f 40 a0 movdqa %xmm0,-0x60(%eax) + 12.31 : 34f1d: 66 0f 7f 40 b0 movdqa %xmm0,-0x50(%eax) + +At a glance, it looks like the time is being spent copying pixmaps to +the card. Further investigation would be needed to determine why pixmaps +are being copied around so much but a starting point would be to take an +ancient build of libpixmap out of the library path where it was totally +forgotten about from months ago! diff --git a/Documentation/trace/tracepoints.rst b/Documentation/trace/tracepoints.rst new file mode 100644 index 000000000..6e3ce3bf3 --- /dev/null +++ b/Documentation/trace/tracepoints.rst @@ -0,0 +1,148 @@ +================================== +Using the Linux Kernel Tracepoints +================================== + +:Author: Mathieu Desnoyers + + +This document introduces Linux Kernel Tracepoints and their use. It +provides examples of how to insert tracepoints in the kernel and +connect probe functions to them and provides some examples of probe +functions. + + +Purpose of tracepoints +---------------------- +A tracepoint placed in code provides a hook to call a function (probe) +that you can provide at runtime. A tracepoint can be "on" (a probe is +connected to it) or "off" (no probe is attached). When a tracepoint is +"off" it has no effect, except for adding a tiny time penalty +(checking a condition for a branch) and space penalty (adding a few +bytes for the function call at the end of the instrumented function +and adds a data structure in a separate section). When a tracepoint +is "on", the function you provide is called each time the tracepoint +is executed, in the execution context of the caller. When the function +provided ends its execution, it returns to the caller (continuing from +the tracepoint site). + +You can put tracepoints at important locations in the code. They are +lightweight hooks that can pass an arbitrary number of parameters, +which prototypes are described in a tracepoint declaration placed in a +header file. + +They can be used for tracing and performance accounting. + + +Usage +----- +Two elements are required for tracepoints : + +- A tracepoint definition, placed in a header file. +- The tracepoint statement, in C code. + +In order to use tracepoints, you should include linux/tracepoint.h. + +In include/trace/events/subsys.h:: + + #undef TRACE_SYSTEM + #define TRACE_SYSTEM subsys + + #if !defined(_TRACE_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) + #define _TRACE_SUBSYS_H + + #include <linux/tracepoint.h> + + DECLARE_TRACE(subsys_eventname, + TP_PROTO(int firstarg, struct task_struct *p), + TP_ARGS(firstarg, p)); + + #endif /* _TRACE_SUBSYS_H */ + + /* This part must be outside protection */ + #include <trace/define_trace.h> + +In subsys/file.c (where the tracing statement must be added):: + + #include <trace/events/subsys.h> + + #define CREATE_TRACE_POINTS + DEFINE_TRACE(subsys_eventname); + + void somefct(void) + { + ... + trace_subsys_eventname(arg, task); + ... + } + +Where : + - subsys_eventname is an identifier unique to your event + + - subsys is the name of your subsystem. + - eventname is the name of the event to trace. + + - `TP_PROTO(int firstarg, struct task_struct *p)` is the prototype of the + function called by this tracepoint. + + - `TP_ARGS(firstarg, p)` are the parameters names, same as found in the + prototype. + + - if you use the header in multiple source files, `#define CREATE_TRACE_POINTS` + should appear only in one source file. + +Connecting a function (probe) to a tracepoint is done by providing a +probe (function to call) for the specific tracepoint through +register_trace_subsys_eventname(). Removing a probe is done through +unregister_trace_subsys_eventname(); it will remove the probe. + +tracepoint_synchronize_unregister() must be called before the end of +the module exit function to make sure there is no caller left using +the probe. This, and the fact that preemption is disabled around the +probe call, make sure that probe removal and module unload are safe. + +The tracepoint mechanism supports inserting multiple instances of the +same tracepoint, but a single definition must be made of a given +tracepoint name over all the kernel to make sure no type conflict will +occur. Name mangling of the tracepoints is done using the prototypes +to make sure typing is correct. Verification of probe type correctness +is done at the registration site by the compiler. Tracepoints can be +put in inline functions, inlined static functions, and unrolled loops +as well as regular functions. + +The naming scheme "subsys_event" is suggested here as a convention +intended to limit collisions. Tracepoint names are global to the +kernel: they are considered as being the same whether they are in the +core kernel image or in modules. + +If the tracepoint has to be used in kernel modules, an +EXPORT_TRACEPOINT_SYMBOL_GPL() or EXPORT_TRACEPOINT_SYMBOL() can be +used to export the defined tracepoints. + +If you need to do a bit of work for a tracepoint parameter, and +that work is only used for the tracepoint, that work can be encapsulated +within an if statement with the following:: + + if (trace_foo_bar_enabled()) { + int i; + int tot = 0; + + for (i = 0; i < count; i++) + tot += calculate_nuggets(); + + trace_foo_bar(tot); + } + +All trace_<tracepoint>() calls have a matching trace_<tracepoint>_enabled() +function defined that returns true if the tracepoint is enabled and +false otherwise. The trace_<tracepoint>() should always be within the +block of the if (trace_<tracepoint>_enabled()) to prevent races between +the tracepoint being enabled and the check being seen. + +The advantage of using the trace_<tracepoint>_enabled() is that it uses +the static_key of the tracepoint to allow the if statement to be implemented +with jump labels and avoid conditional branches. + +.. note:: The convenience macro TRACE_EVENT provides an alternative way to + define tracepoints. Check http://lwn.net/Articles/379903, + http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362 + for a series of articles with more details. diff --git a/Documentation/trace/uprobetracer.rst b/Documentation/trace/uprobetracer.rst new file mode 100644 index 000000000..d08228115 --- /dev/null +++ b/Documentation/trace/uprobetracer.rst @@ -0,0 +1,173 @@ +========================================= +Uprobe-tracer: Uprobe-based Event Tracing +========================================= + +:Author: Srikar Dronamraju + + +Overview +-------- +Uprobe based trace events are similar to kprobe based trace events. +To enable this feature, build your kernel with CONFIG_UPROBE_EVENTS=y. + +Similar to the kprobe-event tracer, this doesn't need to be activated via +current_tracer. Instead of that, add probe points via +/sys/kernel/debug/tracing/uprobe_events, and enable it via +/sys/kernel/debug/tracing/events/uprobes/<EVENT>/enable. + +However unlike kprobe-event tracer, the uprobe event interface expects the +user to calculate the offset of the probepoint in the object. + +Synopsis of uprobe_tracer +------------------------- +:: + + p[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a uprobe + r[:[GRP/]EVENT] PATH:OFFSET [FETCHARGS] : Set a return uprobe (uretprobe) + -:[GRP/]EVENT : Clear uprobe or uretprobe event + + GRP : Group name. If omitted, "uprobes" is the default value. + EVENT : Event name. If omitted, the event name is generated based + on PATH+OFFSET. + PATH : Path to an executable or a library. + OFFSET : Offset where the probe is inserted. + + FETCHARGS : Arguments. Each probe can have up to 128 args. + %REG : Fetch register REG + @ADDR : Fetch memory at ADDR (ADDR should be in userspace) + @+OFFSET : Fetch memory at OFFSET (OFFSET from same file as PATH) + $stackN : Fetch Nth entry of stack (N >= 0) + $stack : Fetch stack address. + $retval : Fetch return value.(*) + $comm : Fetch current task comm. + +|-offs(FETCHARG) : Fetch memory at FETCHARG +|- offs address.(**) + NAME=FETCHARG : Set NAME as the argument name of FETCHARG. + FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types + (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types + (x8/x16/x32/x64), "string" and bitfield are supported. + + (*) only for return probe. + (**) this is useful for fetching a field of data structures. + +Types +----- +Several types are supported for fetch-args. Uprobe tracer will access memory +by given type. Prefix 's' and 'u' means those types are signed and unsigned +respectively. 'x' prefix implies it is unsigned. Traced arguments are shown +in decimal ('s' and 'u') or hexadecimal ('x'). Without type casting, 'x32' +or 'x64' is used depends on the architecture (e.g. x86-32 uses x32, and +x86-64 uses x64). +String type is a special type, which fetches a "null-terminated" string from +user space. +Bitfield is another special type, which takes 3 parameters, bit-width, bit- +offset, and container-size (usually 32). The syntax is:: + + b<bit-width>@<bit-offset>/<container-size> + +For $comm, the default type is "string"; any other type is invalid. + + +Event Profiling +--------------- +You can check the total number of probe hits and probe miss-hits via +/sys/kernel/debug/tracing/uprobe_profile. +The first column is event name, the second is the number of probe hits, +the third is the number of probe miss-hits. + +Usage examples +-------------- + * Add a probe as a new uprobe event, write a new definition to uprobe_events + as below (sets a uprobe at an offset of 0x4245c0 in the executable /bin/bash):: + + echo 'p /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events + + * Add a probe as a new uretprobe event:: + + echo 'r /bin/bash:0x4245c0' > /sys/kernel/debug/tracing/uprobe_events + + * Unset registered event:: + + echo '-:p_bash_0x4245c0' >> /sys/kernel/debug/tracing/uprobe_events + + * Print out the events that are registered:: + + cat /sys/kernel/debug/tracing/uprobe_events + + * Clear all events:: + + echo > /sys/kernel/debug/tracing/uprobe_events + +Following example shows how to dump the instruction pointer and %ax register +at the probed text address. Probe zfree function in /bin/zsh:: + + # cd /sys/kernel/debug/tracing/ + # cat /proc/`pgrep zsh`/maps | grep /bin/zsh | grep r-xp + 00400000-0048a000 r-xp 00000000 08:03 130904 /bin/zsh + # objdump -T /bin/zsh | grep -w zfree + 0000000000446420 g DF .text 0000000000000012 Base zfree + +0x46420 is the offset of zfree in object /bin/zsh that is loaded at +0x00400000. Hence the command to uprobe would be:: + + # echo 'p:zfree_entry /bin/zsh:0x46420 %ip %ax' > uprobe_events + +And the same for the uretprobe would be:: + + # echo 'r:zfree_exit /bin/zsh:0x46420 %ip %ax' >> uprobe_events + +.. note:: User has to explicitly calculate the offset of the probe-point + in the object. + +We can see the events that are registered by looking at the uprobe_events file. +:: + + # cat uprobe_events + p:uprobes/zfree_entry /bin/zsh:0x00046420 arg1=%ip arg2=%ax + r:uprobes/zfree_exit /bin/zsh:0x00046420 arg1=%ip arg2=%ax + +Format of events can be seen by viewing the file events/uprobes/zfree_entry/format. +:: + + # cat events/uprobes/zfree_entry/format + name: zfree_entry + ID: 922 + format: + field:unsigned short common_type; offset:0; size:2; signed:0; + field:unsigned char common_flags; offset:2; size:1; signed:0; + field:unsigned char common_preempt_count; offset:3; size:1; signed:0; + field:int common_pid; offset:4; size:4; signed:1; + field:int common_padding; offset:8; size:4; signed:1; + + field:unsigned long __probe_ip; offset:12; size:4; signed:0; + field:u32 arg1; offset:16; size:4; signed:0; + field:u32 arg2; offset:20; size:4; signed:0; + + print fmt: "(%lx) arg1=%lx arg2=%lx", REC->__probe_ip, REC->arg1, REC->arg2 + +Right after definition, each event is disabled by default. For tracing these +events, you need to enable it by:: + + # echo 1 > events/uprobes/enable + +Lets disable the event after sleeping for some time. +:: + + # sleep 20 + # echo 0 > events/uprobes/enable + +And you can see the traced information via /sys/kernel/debug/tracing/trace. +:: + + # cat trace + # tracer: nop + # + # TASK-PID CPU# TIMESTAMP FUNCTION + # | | | | | + zsh-24842 [006] 258544.995456: zfree_entry: (0x446420) arg1=446420 arg2=79 + zsh-24842 [007] 258545.000270: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 + zsh-24842 [002] 258545.043929: zfree_entry: (0x446420) arg1=446420 arg2=79 + zsh-24842 [004] 258547.046129: zfree_exit: (0x446540 <- 0x446420) arg1=446540 arg2=0 + +Output shows us uprobe was triggered for a pid 24842 with ip being 0x446420 +and contents of ax register being 79. And uretprobe was triggered with ip at +0x446540 with counterpart function entry at 0x446420. |