From 88238513bb26713ef6d4418bdf1af062fe608bcb Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Google)" Date: Tue, 17 Jan 2023 10:21:30 -0500 Subject: tracing/histogram: Document variable stacktrace Add a little documentation (and a useful example) of how a stacktrace can be used within a histogram variable and synthetic event. Link: https://lkml.kernel.org/r/20230117152236.320181354@goodmis.org Cc: Masami Hiramatsu Cc: Andrew Morton Cc: Tom Zanussi Cc: Ross Zwisler Cc: Ching-lin Yu Signed-off-by: Steven Rostedt (Google) --- Documentation/trace/histogram.rst | 129 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+) (limited to 'Documentation/trace/histogram.rst') diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index f95459aa984f..5c391328b9bb 100644 --- a/Documentation/trace/histogram.rst +++ b/Documentation/trace/histogram.rst @@ -81,6 +81,7 @@ Documentation written by Tom Zanussi .usecs display a common_timestamp in microseconds .percent display a number of percentage value .graph display a bar-graph of a value + .stacktrace display as a stacktrace (must by a long[] type) ============= ================================================= Note that in general the semantics of a given field aren't @@ -1786,6 +1787,8 @@ or assigned to a variable and referenced in a subsequent expression:: # echo 'hist:keys=next_pid:us_per_sec=1000000 ...' >> event/trigger # echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/$us_per_sec ...' >> event/trigger +Variables can even hold stacktraces, which are useful with synthetic events. + 2.2.2 Synthetic Events ---------------------- @@ -1940,6 +1943,132 @@ the ".buckets" modifier and specify a size (in this case groups of 10). Entries: 16 Dropped: 0 +To save stacktraces, create a synthetic event with a field of type "unsigned long[]" +or even just "long[]". For example, to see how long a task is blocked in an +uninterruptible state: + + # cd /sys/kernel/tracing + # echo 's:block_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events + # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=stacktrace if prev_state == 2' >> events/sched/sched_switch/trigger + # echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(block_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger + # echo 1 > events/synthetic/block_lat/enable + # 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 + # | | | ||||| | | + -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 + +A synthetic event that has a stacktrace field may use it as a key in histogram: + + # echo 'hist:delta.buckets=100,stack.stacktrace:sort=delta' > events/synthetic/block_lat/trigger + # cat events/synthetic/block_lat/hist + + # event histogram + # + # trigger info: hist:keys=delta.buckets=100,stacktrace:vals=hitcount:sort=delta.buckets=100:size=2048 [active] + # + + { delta: ~ 0-99, stacktrace: + event_hist_trigger+0x464/0x480 + event_triggers_call+0x52/0xe0 + trace_event_buffer_commit+0x193/0x250 + trace_event_raw_event_sched_switch+0xfc/0x150 + __traceiter_sched_switch+0x41/0x60 + __schedule+0x448/0x7b0 + schedule_idle+0x26/0x40 + cpu_startup_entry+0x19/0x20 + start_secondary+0xed/0xf0 + secondary_startup_64_no_verify+0xe0/0xeb + } hitcount: 6 + { delta: ~ 0-99, stacktrace: + event_hist_trigger+0x464/0x480 + event_triggers_call+0x52/0xe0 + trace_event_buffer_commit+0x193/0x250 + trace_event_raw_event_sched_switch+0xfc/0x150 + __traceiter_sched_switch+0x41/0x60 + __schedule+0x448/0x7b0 + schedule_idle+0x26/0x40 + cpu_startup_entry+0x19/0x20 + __pfx_kernel_init+0x0/0x10 + arch_call_rest_init+0xa/0x24 + start_kernel+0x964/0x98d + secondary_startup_64_no_verify+0xe0/0xeb + } hitcount: 3 + { delta: ~ 0-99, stacktrace: + event_hist_trigger+0x464/0x480 + event_triggers_call+0x52/0xe0 + trace_event_buffer_commit+0x193/0x250 + trace_event_raw_event_sched_switch+0xfc/0x150 + __traceiter_sched_switch+0x41/0x60 + __schedule+0x448/0x7b0 + schedule+0x5a/0xb0 + worker_thread+0xaf/0x380 + kthread+0xe9/0x110 + ret_from_fork+0x2c/0x50 + } hitcount: 1 + { delta: ~ 100-199, stacktrace: + event_hist_trigger+0x464/0x480 + event_triggers_call+0x52/0xe0 + trace_event_buffer_commit+0x193/0x250 + trace_event_raw_event_sched_switch+0xfc/0x150 + __traceiter_sched_switch+0x41/0x60 + __schedule+0x448/0x7b0 + schedule_idle+0x26/0x40 + cpu_startup_entry+0x19/0x20 + start_secondary+0xed/0xf0 + secondary_startup_64_no_verify+0xe0/0xeb + } hitcount: 15 + [..] + { delta: ~ 8500-8599, stacktrace: + event_hist_trigger+0x464/0x480 + event_triggers_call+0x52/0xe0 + trace_event_buffer_commit+0x193/0x250 + trace_event_raw_event_sched_switch+0xfc/0x150 + __traceiter_sched_switch+0x41/0x60 + __schedule+0x448/0x7b0 + schedule_idle+0x26/0x40 + cpu_startup_entry+0x19/0x20 + start_secondary+0xed/0xf0 + secondary_startup_64_no_verify+0xe0/0xeb + } hitcount: 1 + + Totals: + Hits: 89 + Entries: 11 + Dropped: 0 + 2.2.3 Hist trigger 'handlers' and 'actions' ------------------------------------------- -- cgit v1.2.3