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diff --git a/src/spdk/doc/nvmf_tracing.md b/src/spdk/doc/nvmf_tracing.md new file mode 100644 index 00000000..4a7b9afb --- /dev/null +++ b/src/spdk/doc/nvmf_tracing.md @@ -0,0 +1,179 @@ +# NVMe-oF Target Tracepoints {#nvmf_tgt_tracepoints} + +# Introduction {#tracepoints_intro} + +SPDK has a tracing framework for capturing low-level event information at runtime. +Tracepoints provide a high-performance tracing mechanism that is accessible at runtime. +They are implemented as a circular buffer in shared memory that is accessible from other +processes. The NVMe-oF target is instrumented with tracepoints to enable analysis of +both performance and application crashes. (Note: the SPDK tracing framework should still +be considered experimental. Work to formalize and document the framework is in progress.) + +# Enabling Tracepoints {#enable_tracepoints} + +Tracepoints are placed in groups. They are enabled and disabled as a group. To enable +the instrumentation of all the tracepoints group in an SPDK target application, start the +target with -e parameter set to 0xFFFF: + +~~~ +app/nvmf_tgt/nvmf_tgt -e 0xFFFF +~~~ + +To enable the instrumentation of just the NVMe-oF RDMA tracepoints in an SPDK target +application, start the target with the -e parameter set to 0x10: + +~~~ +app/nvmf_tgt/nvmf_tgt -e 0x10 +~~~ + +When the target starts, a message is logged with the information you need to view +the tracepoints in a human-readable format using the spdk_trace application. The target +will also log information about the shared memory file. + +~~~{.sh} +app.c: 527:spdk_app_setup_trace: *NOTICE*: Tracepoint Group Mask 0xFFFF specified. +app.c: 531:spdk_app_setup_trace: *NOTICE*: Use 'spdk_trace -s nvmf -p 24147' to capture a snapshot of events at runtime. +app.c: 533:spdk_app_setup_trace: *NOTICE*: Or copy /dev/shm/nvmf_trace.pid24147 for offline analysis/debug. +~~~ + +Note that when tracepoints are enabled, the shared memory files are not deleted when the application +exits. This ensures the file can be used for analysis after the application exits. On Linux, the +shared memory files are in /dev/shm, and can be deleted manually to free shm space if needed. A system +reboot will also free all of the /dev/shm files. + +# Capturing a snapshot of events {#capture_tracepoints} + +Send I/Os to the SPDK target application to generate events. The following is +an example usage of perf to send I/Os to the NVMe-oF target over an RDMA network +interface for 10 minutes. + +~~~ +./perf -q 128 -s 4096 -w randread -t 600 -r 'trtype:RDMA adrfam:IPv4 traddr:192.168.100.2 trsvcid:4420' +~~~ + +The spdk_trace program can be found in the app/trace directory. To analyze the tracepoints on the same +system running the NVMe-oF target, simply execute the command line shown in the log: + +~~~{.sh} +app/trace/spdk_trace -s nvmf -p 24147 +~~~ + +To analyze the tracepoints on a different system, first prepare the tracepoint file for transfer. The +tracepoint file can be large, but usually compresses very well. This step can also be used to prepare +a tracepoint file to attach to a GitHub issue for debugging NVMe-oF application crashes. + +~~~{.sh} +bzip2 -c /dev/shm/nvmf_trace.pid24147 > /tmp/trace.bz2 +~~~ + +After transferring the /tmp/trace.bz2 tracepoint file to a different system: + +~~~{.sh} +bunzip2 /tmp/trace.bz2 +app/trace/spdk_trace -f /tmp/trace +~~~ + +The following is sample trace capture showing the cumulative time that each +I/O spends at each RDMA state. All the trace captures with the same id are for +the same I/O. + +~~~ +28: 6026.658 ( 12656064) RDMA_REQ_NEED_BUFFER id: r3622 time: 0.019 +28: 6026.694 ( 12656140) RDMA_REQ_RDY_TO_EXECUTE id: r3622 time: 0.055 +28: 6026.820 ( 12656406) RDMA_REQ_EXECUTING id: r3622 time: 0.182 +28: 6026.992 ( 12656766) RDMA_REQ_EXECUTED id: r3477 time: 228.510 +28: 6027.010 ( 12656804) RDMA_REQ_TX_PENDING_C_TO_H id: r3477 time: 228.528 +28: 6027.022 ( 12656828) RDMA_REQ_RDY_TO_COMPLETE id: r3477 time: 228.539 +28: 6027.115 ( 12657024) RDMA_REQ_COMPLETING id: r3477 time: 228.633 +28: 6027.471 ( 12657770) RDMA_REQ_COMPLETED id: r3518 time: 171.577 +28: 6028.027 ( 12658940) RDMA_REQ_NEW id: r3623 +28: 6028.057 ( 12659002) RDMA_REQ_NEED_BUFFER id: r3623 time: 0.030 +28: 6028.095 ( 12659082) RDMA_REQ_RDY_TO_EXECUTE id: r3623 time: 0.068 +28: 6028.216 ( 12659336) RDMA_REQ_EXECUTING id: r3623 time: 0.189 +28: 6028.408 ( 12659740) RDMA_REQ_EXECUTED id: r3505 time: 190.509 +28: 6028.441 ( 12659808) RDMA_REQ_TX_PENDING_C_TO_H id: r3505 time: 190.542 +28: 6028.452 ( 12659832) RDMA_REQ_RDY_TO_COMPLETE id: r3505 time: 190.553 +28: 6028.536 ( 12660008) RDMA_REQ_COMPLETING id: r3505 time: 190.637 +28: 6028.854 ( 12660676) RDMA_REQ_COMPLETED id: r3465 time: 247.000 +28: 6029.433 ( 12661892) RDMA_REQ_NEW id: r3624 +28: 6029.452 ( 12661932) RDMA_REQ_NEED_BUFFER id: r3624 time: 0.019 +28: 6029.482 ( 12661996) RDMA_REQ_RDY_TO_EXECUTE id: r3624 time: 0.050 +28: 6029.591 ( 12662224) RDMA_REQ_EXECUTING id: r3624 time: 0.158 +28: 6029.782 ( 12662624) RDMA_REQ_EXECUTED id: r3564 time: 96.937 +28: 6029.798 ( 12662658) RDMA_REQ_TX_PENDING_C_TO_H id: r3564 time: 96.953 +28: 6029.812 ( 12662688) RDMA_REQ_RDY_TO_COMPLETE id: r3564 time: 96.967 +28: 6029.899 ( 12662870) RDMA_REQ_COMPLETING id: r3564 time: 97.054 +28: 6030.262 ( 12663634) RDMA_REQ_COMPLETED id: r3477 time: 231.780 +28: 6030.786 ( 12664734) RDMA_REQ_NEW id: r3625 +28: 6030.804 ( 12664772) RDMA_REQ_NEED_BUFFER id: r3625 time: 0.018 +28: 6030.841 ( 12664848) RDMA_REQ_RDY_TO_EXECUTE id: r3625 time: 0.054 +28: 6030.963 ( 12665104) RDMA_REQ_EXECUTING id: r3625 time: 0.176 +28: 6031.139 ( 12665474) RDMA_REQ_EXECUTED id: r3552 time: 114.906 +28: 6031.196 ( 12665594) RDMA_REQ_TX_PENDING_C_TO_H id: r3552 time: 114.963 +28: 6031.210 ( 12665624) RDMA_REQ_RDY_TO_COMPLETE id: r3552 time: 114.977 +28: 6031.293 ( 12665798) RDMA_REQ_COMPLETING id: r3552 time: 115.060 +28: 6031.633 ( 12666512) RDMA_REQ_COMPLETED id: r3505 time: 193.734 +28: 6032.230 ( 12667766) RDMA_REQ_NEW id: r3626 +28: 6032.248 ( 12667804) RDMA_REQ_NEED_BUFFER id: r3626 time: 0.018 +28: 6032.288 ( 12667888) RDMA_REQ_RDY_TO_EXECUTE id: r3626 time: 0.058 +28: 6032.396 ( 12668114) RDMA_REQ_EXECUTING id: r3626 time: 0.166 +28: 6032.593 ( 12668528) RDMA_REQ_EXECUTED id: r3570 time: 90.443 +28: 6032.611 ( 12668564) RDMA_REQ_TX_PENDING_C_TO_H id: r3570 time: 90.460 +28: 6032.623 ( 12668590) RDMA_REQ_RDY_TO_COMPLETE id: r3570 time: 90.473 +28: 6032.707 ( 12668766) RDMA_REQ_COMPLETING id: r3570 time: 90.557 +28: 6033.056 ( 12669500) RDMA_REQ_COMPLETED id: r3564 time: 100.211 +~~~ + +# Adding New Tracepoints {#add_tracepoints} + +SPDK applications and libraries provide several trace points. You can add new +tracepoints to the existing trace groups. For example, to add a new tracepoints +to the SPDK RDMA library (lib/nvmf/rdma.c) trace group TRACE_GROUP_NVMF_RDMA, +define the tracepoints and assigning them a unique ID using the SPDK_TPOINT_ID macro: + +~~~ +#define TRACE_GROUP_NVMF_RDMA 0x4 +#define TRACE_RDMA_REQUEST_STATE_NEW SPDK_TPOINT_ID(TRACE_GROUP_NVMF_RDMA, 0x0) +... +#define NEW_TRACE_POINT_NAME SPDK_TPOINT_ID(TRACE_GROUP_NVMF_RDMA, UNIQUE_ID) +~~~ + +You also need to register the new trace points in the SPDK_TRACE_REGISTER_FN macro call +within the application/library using the spdk_trace_register_description function +as shown below: + +~~~ +SPDK_TRACE_REGISTER_FN(nvmf_trace) +{ + spdk_trace_register_object(OBJECT_NVMF_RDMA_IO, 'r'); + spdk_trace_register_description("RDMA_REQ_NEW", "", + TRACE_RDMA_REQUEST_STATE_NEW, + OWNER_NONE, OBJECT_NVMF_RDMA_IO, 1, 1, "cmid: "); + ... + spdk_trace_register_description("NEW_RDMA_REQ_NAME", "", + NEW_TRACE_POINT_NAME, + OWNER_NONE, OBJECT_NVMF_RDMA_IO, 0, 1, "cmid: "); +} +~~~ + +Finally, use the spdk_trace_record function at the appropriate point in the +application/library to record the current trace state for the new trace points. +The following example shows the usage of the spdk_trace_record function to +record the current trace state of several tracepoints. + +~~~ + case RDMA_REQUEST_STATE_NEW: + spdk_trace_record(TRACE_RDMA_REQUEST_STATE_NEW, 0, 0, (uintptr_t)rdma_req, (uintptr_t)rqpair->cm_id); + ... + break; + case RDMA_REQUEST_STATE_NEED_BUFFER: + spdk_trace_record(TRACE_RDMA_REQUEST_STATE_NEED_BUFFER, 0, 0, (uintptr_t)rdma_req, (uintptr_t)rqpair->cm_id); + ... + break; + case RDMA_REQUEST_STATE_TRANSFER_PENDING_HOST_TO_CONTROLLER: + spdk_trace_record(TRACE_RDMA_REQUEST_STATE_TRANSFER_PENDING_HOST_TO_CONTROLLER, 0, 0, + (uintptr_t)rdma_req, (uintptr_t)rqpair->cm_id); + ... +~~~ + +All the tracing functions are documented in the [Tracepoint library documentation](https://www.spdk.io/doc/trace_8h.html) |