Messages in this thread Patch in this message | | | Subject | [PATCH] perf_counter: Report the cloning task as parent on perf_counter_fork() | From | Peter Zijlstra <> | Date | Thu, 13 Aug 2009 16:14:42 +0200 |
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A bug in (9f498cc: perf_counter: Full task tracing) makes profiling multi-threaded apps it go belly up.
[ output as: (PID:TID):(PPID:PTID) ]
# ./perf report -D | grep FORK 0x4b0 [0x18]: PERF_EVENT_FORK: (3237:3237):(3236:3236) 0xa10 [0x18]: PERF_EVENT_FORK: (3237:3238):(3236:3236) 0xa70 [0x18]: PERF_EVENT_FORK: (3237:3239):(3236:3236) 0xad0 [0x18]: PERF_EVENT_FORK: (3237:3240):(3236:3236) 0xb18 [0x18]: PERF_EVENT_FORK: (3237:3241):(3236:3236)
Shows us that the test (27d028d perf report: Update for the new FORK/EXIT events) in builtin-report.c:
/* * A thread clone will have the same PID for both * parent and child. */ if (thread == parent) return 0;
Will clearly fail.
The problem is that perf_counter_fork() reports the actual parent, instead of the cloning thread.
Fixing that (with the below patch), yields:
# ./perf report -D | grep FORK 0x4c8 [0x18]: PERF_EVENT_FORK: (1590:1590):(1589:1589) 0xbd8 [0x18]: PERF_EVENT_FORK: (1590:1591):(1590:1590) 0xc80 [0x18]: PERF_EVENT_FORK: (1590:1592):(1590:1590) 0x3338 [0x18]: PERF_EVENT_FORK: (1590:1593):(1590:1590) 0x66b0 [0x18]: PERF_EVENT_FORK: (1590:1594):(1590:1590)
Which both makes more sense and doesn't confuse perf report anymore.
Reported-by: Pekka Enberg <penberg@cs.helsinki.fi> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> --- perf_counter.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
Index: linux-2.6/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/kernel/perf_counter.c +++ linux-2.6/kernel/perf_counter.c @@ -3024,10 +3024,10 @@ static void perf_counter_task_output(str return; task_event->event.pid = perf_counter_pid(counter, task); - task_event->event.ppid = perf_counter_pid(counter, task->real_parent); + task_event->event.ppid = perf_counter_pid(counter, current); task_event->event.tid = perf_counter_tid(counter, task); - task_event->event.ptid = perf_counter_tid(counter, task->real_parent); + task_event->event.ptid = perf_counter_tid(counter, current); perf_output_put(&handle, task_event->event); perf_output_end(&handle);
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