On Tuesday, January 16, 2018 1:40:38 PM CET Cheng Jian wrote: > When i use perf to trace the sched_wakeup_new tracepoint, there is > a bug that output the same event repetitiously. > It can be reproduced by : > > #./test_fork > parent pid : 1059 > child pid : 1060 > #perf record -e sched:sched_wakeup_new -p 1060 > > test_fork is an demo that can generating wakeup_new event, parent > process does nothing but fork a child process, and then they both > quit. > > There are 4 processors in this machine. before this patch, > perf script(perf-1058, parent-1059, child-1060) : > > test_fork 1059 [001] 62.913689: sched:sched_wakeup_new: > comm=test_fork pid=1060 prio=120 target_cpu=002 test_fork 1059 [001] > 62.913698: sched:sched_wakeup_new: comm=test_fork pid=1060 prio=120 > target_cpu=002 test_fork 1059 [001] 62.913705: sched:sched_wakeup_new: > comm=test_fork pid=1060 prio=120 target_cpu=002 > > but ftrace report this event only once : > > test_fork-1059 [002] d... 62.913680: sched_wakeup_new: comm=test_fork > pid=1060 prio=120 target_cpu=002 > > perf script print the same wakeup_new event multiple times. > > These events which trigger this issue all specify a target process. > commit e6dab5ffab59 ("perf/trace: Add ability to set a target task > for events") has designed a method to trace these events. For > example, the sched_wakeup and sched_wakeup_new tracepoint will be > caught when the current task wakeup a target task. > > These events are registered as per cpu most of the time and attached > to the task too, we will get all of them from the perf_event_context > of this task, they will be matched success but are all the same event. > So check the cpu number of this event to avoid matching them multiple > times. > > after this patch, perf script(parent-1040, child-1041): > > test_fork 1040 [002] 36.536079: sched:sched_wakeup_new: > comm=test_fork > pid=1041 prio=120 target_cpu=003 > > It will match it only once for tracing task(child-1041).
Oh, this sounds awesome. I don't have the setup available to compile a kernel with this patch applied, but I think from the description it solves a long- standing issue with perf's sleep-time profiling. Can someone try this please: https://perf.wiki.kernel.org/index.php/Tutorial#Profiling_sleep_times Use 'sleep 1' as the debuggee. On my system, I get the period multiplied by nproc like you describe: ``` $ perf-sleep-record sleep 1 .. $ perf report --stdio --show-total-period | grep "Event count" .. # Event count (approx.): 8000845488 $ nproc 8 ``` The sleep-record script is available at: https://github.com/milianw/shell-helpers/blob/master/perf-sleep-record I believe your patch also fixes the sched_stat_* tracepoints to be only emitted once per CPU. Can you verify this? I.e. is the period finally correctly calculated and we get a value of roughly 1E9ns == 1s? Thanks -- Milian Wolff | milian.wo...@kdab.com | Senior Software Engineer KDAB (Deutschland) GmbH, a KDAB Group company Tel: +49-30-521325470 KDAB - The Qt, C++ and OpenGL Experts
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