| Message ID | 20230117044010.838685230@goodmis.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | tracing/histograms: Pass stacktrace from synthetic start event to end event | expand |
Bah, I forgot to Cc, Tom. Tom, here's the lore link: https://lore.kernel.org/linux-trace-kernel/20230117044010.838685230@goodmis.org/T/#m116ab617cc475b68589f42a0cfd6c1b2029b0e39 -- Steve On Mon, 16 Jan 2023 23:40:10 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > 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
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