Messages in this thread | | | Date | Mon, 16 Jan 2023 23:40:10 -0500 | From | Steven Rostedt <> | Subject | [PATCH 0/5] tracing/histograms: Pass stacktrace from synthetic start event to end event |
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I finally got around to implementing what I've been wanting to do for a long time! That is to pass stacktraces from the start to the end event of a synthetic event. Specifically, I need to get the stacktrace of a task as it schedules out, but I don't want to see it until it schedules back in and I check the timings to show that it is longer than normal. That is now done with:
# echo 's:block_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=stacktrace if prev_state == 2' >> events/sched/sched_switch/trigger # echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(block_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger
The above creates a synthetic event that will trigger on the max delta of a task blocked in an uninterruptible state. It will show you the stack trace of where that occurred!
# echo 1 > events/synthetic/block_lat/enable # ls -lR > /dev/null # cat trace
# tracer: nop # # entries-in-buffer/entries-written: 2/2 #P:8 # # _-----=> irqs-off/BH-disabled # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / _-=> migrate-disable # |||| / delay # TASK-PID CPU# ||||| TIMESTAMP FUNCTION # | | | ||||| | | <idle>-0 [005] d..4. 521.164922: block_lat: pid=0 delta=8322 stack=STACK: => __schedule+0x448/0x7b0 => schedule+0x5a/0xb0 => io_schedule+0x42/0x70 => bit_wait_io+0xd/0x60 => __wait_on_bit+0x4b/0x140 => out_of_line_wait_on_bit+0x91/0xb0 => jbd2_journal_commit_transaction+0x1679/0x1a70 => kjournald2+0xa9/0x280 => kthread+0xe9/0x110 => ret_from_fork+0x2c/0x50
<...>-2 [004] d..4. 525.184257: block_lat: pid=2 delta=76 stack=STACK: => __schedule+0x448/0x7b0 => schedule+0x5a/0xb0 => schedule_timeout+0x11a/0x150 => wait_for_completion_killable+0x144/0x1f0 => __kthread_create_on_node+0xe7/0x1e0 => kthread_create_on_node+0x51/0x70 => create_worker+0xcc/0x1a0 => worker_thread+0x2ad/0x380 => kthread+0xe9/0x110 => ret_from_fork+0x2c/0x50
Steven Rostedt (Google) (5): tracing: Simplify calculating entry size using struct_size() tracing: Allow stacktraces to be saved as histogram variables tracing: Allow synthetic events to pass around stacktraces tracing/histogram: Document variable stacktrace tracing/histogram: Add simple tests for stacktrace usage of synthetic events
---- Documentation/trace/histogram.rst | 49 +++++++++++++ kernel/trace/trace.c | 2 +- kernel/trace/trace.h | 4 ++ kernel/trace/trace_events_hist.c | 42 ++++++++--- kernel/trace/trace_events_synth.c | 83 +++++++++++++++++++++- kernel/trace/trace_synth.h | 1 + .../inter-event/trigger-synthetic-event-stack.tc | 24 +++++++ .../inter-event/trigger-synthetic-event-syntax.tc | 6 ++ 8 files changed, 196 insertions(+), 15 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-synthetic-event-stack.tc
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