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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/trace/boottime-trace.rst | |
parent | Initial commit. (diff) | |
download | linux-430c2fc249ea5c0536abd21c23382884005c9093.tar.xz linux-430c2fc249ea5c0536abd21c23382884005c9093.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/trace/boottime-trace.rst')
-rw-r--r-- | Documentation/trace/boottime-trace.rst | 222 |
1 files changed, 222 insertions, 0 deletions
diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst new file mode 100644 index 000000000..89b643349 --- /dev/null +++ b/Documentation/trace/boottime-trace.rst @@ -0,0 +1,222 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================= +Boot-time tracing +================= + +:Author: Masami Hiramatsu <mhiramat@kernel.org> + +Overview +======== + +Boot-time tracing allows users to trace boot-time process including +device initialization with full features of ftrace including per-event +filter and actions, histograms, kprobe-events and synthetic-events, +and trace instances. +Since kernel command line is not enough to control these complex features, +this uses bootconfig file to describe tracing feature programming. + +Options in the Boot Config +========================== + +Here is the list of available options list for boot time tracing in +boot config file [1]_. All options are under "ftrace." or "kernel." +prefix. See kernel parameters for the options which starts +with "kernel." prefix [2]_. + +.. [1] See :ref:`Documentation/admin-guide/bootconfig.rst <bootconfig>` +.. [2] See :ref:`Documentation/admin-guide/kernel-parameters.rst <kernelparameters>` + +Ftrace Global Options +--------------------- + +Ftrace global options have "kernel." prefix in boot config, which means +these options are passed as a part of kernel legacy command line. + +kernel.tp_printk + Output trace-event data on printk buffer too. + +kernel.dump_on_oops [= MODE] + Dump ftrace on Oops. If MODE = 1 or omitted, dump trace buffer + on all CPUs. If MODE = 2, dump a buffer on a CPU which kicks Oops. + +kernel.traceoff_on_warning + Stop tracing if WARN_ON() occurs. + +kernel.fgraph_max_depth = MAX_DEPTH + Set MAX_DEPTH to maximum depth of fgraph tracer. + +kernel.fgraph_filters = FILTER[, FILTER2...] + Add fgraph tracing function filters. + +kernel.fgraph_notraces = FILTER[, FILTER2...] + Add fgraph non-tracing function filters. + + +Ftrace Per-instance Options +--------------------------- + +These options can be used for each instance including global ftrace node. + +ftrace.[instance.INSTANCE.]options = OPT1[, OPT2[...]] + Enable given ftrace options. + +ftrace.[instance.INSTANCE.]tracing_on = 0|1 + Enable/Disable tracing on this instance when starting boot-time tracing. + (you can enable it by the "traceon" event trigger action) + +ftrace.[instance.INSTANCE.]trace_clock = CLOCK + Set given CLOCK to ftrace's trace_clock. + +ftrace.[instance.INSTANCE.]buffer_size = SIZE + Configure ftrace buffer size to SIZE. You can use "KB" or "MB" + for that SIZE. + +ftrace.[instance.INSTANCE.]alloc_snapshot + Allocate snapshot buffer. + +ftrace.[instance.INSTANCE.]cpumask = CPUMASK + Set CPUMASK as trace cpu-mask. + +ftrace.[instance.INSTANCE.]events = EVENT[, EVENT2[...]] + Enable given events on boot. You can use a wild card in EVENT. + +ftrace.[instance.INSTANCE.]tracer = TRACER + Set TRACER to current tracer on boot. (e.g. function) + +ftrace.[instance.INSTANCE.]ftrace.filters + This will take an array of tracing function filter rules. + +ftrace.[instance.INSTANCE.]ftrace.notraces + This will take an array of NON-tracing function filter rules. + + +Ftrace Per-Event Options +------------------------ + +These options are setting per-event options. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.enable + Enable GROUP:EVENT tracing. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.filter = FILTER + Set FILTER rule to the GROUP:EVENT. + +ftrace.[instance.INSTANCE.]event.GROUP.EVENT.actions = ACTION[, ACTION2[...]] + Set ACTIONs to the GROUP:EVENT. + +ftrace.[instance.INSTANCE.]event.kprobes.EVENT.probes = PROBE[, PROBE2[...]] + Defines new kprobe event based on PROBEs. It is able to define + multiple probes on one event, but those must have same type of + arguments. This option is available only for the event which + group name is "kprobes". + +ftrace.[instance.INSTANCE.]event.synthetic.EVENT.fields = FIELD[, FIELD2[...]] + Defines new synthetic event with FIELDs. Each field should be + "type varname". + +Note that kprobe and synthetic event definitions can be written under +instance node, but those are also visible from other instances. So please +take care for event name conflict. + + +When to Start +============= + +All boot-time tracing options starting with ``ftrace`` will be enabled at the +end of core_initcall. This means you can trace the events from postcore_initcall. +Most of the subsystems and architecture dependent drivers will be initialized +after that (arch_initcall or subsys_initcall). Thus, you can trace those with +boot-time tracing. +If you want to trace events before core_initcall, you can use the options +starting with ``kernel``. Some of them will be enabled eariler than the initcall +processing (for example,. ``kernel.ftrace=function`` and ``kernel.trace_event`` +will start before the initcall.) + + +Examples +======== + +For example, to add filter and actions for each event, define kprobe +events, and synthetic events with histogram, write a boot config like +below:: + + ftrace.event { + task.task_newtask { + filter = "pid < 128" + enable + } + kprobes.vfs_read { + probes = "vfs_read $arg1 $arg2" + filter = "common_pid < 200" + enable + } + synthetic.initcall_latency { + fields = "unsigned long func", "u64 lat" + actions = "hist:keys=func.sym,lat:vals=lat:sort=lat" + } + initcall.initcall_start { + actions = "hist:keys=func:ts0=common_timestamp.usecs" + } + initcall.initcall_finish { + actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)" + } + } + +Also, boot-time tracing supports "instance" node, which allows us to run +several tracers for different purpose at once. For example, one tracer +is for tracing functions starting with "user\_", and others tracing +"kernel\_" functions, you can write boot config as below:: + + ftrace.instance { + foo { + tracer = "function" + ftrace.filters = "user_*" + } + bar { + tracer = "function" + ftrace.filters = "kernel_*" + } + } + +The instance node also accepts event nodes so that each instance +can customize its event tracing. + +With the trigger action and kprobes, you can trace function-graph while +a function is called. For example, this will trace all function calls in +the pci_proc_init():: + + ftrace { + tracing_on = 0 + tracer = function_graph + event.kprobes { + start_event { + probes = "pci_proc_init" + actions = "traceon" + } + end_event { + probes = "pci_proc_init%return" + actions = "traceoff" + } + } + } + + +This boot-time tracing also supports ftrace kernel parameters via boot +config. +For example, following kernel parameters:: + + trace_options=sym-addr trace_event=initcall:* tp_printk trace_buf_size=1M ftrace=function ftrace_filter="vfs*" + +This can be written in boot config like below:: + + kernel { + trace_options = sym-addr + trace_event = "initcall:*" + tp_printk + trace_buf_size = 1M + ftrace = function + ftrace_filter = "vfs*" + } + +Note that parameters start with "kernel" prefix instead of "ftrace". |