linux-kernel - Re: [PATCH v3] perf/trace : Fix repetitious traces of perf on tracepoint

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Date:   Sat, 27 Jan 2018 17:42:19 +0800
From:   "chengjian (D)" <cj.chengjian@...wei.com>
To:     Milian Wolff <milian.wolff@...b.com>
CC:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <jolsa@...hat.com>,
        <namhyung@...nel.org>, <xiexiuqi@...wei.com>,
        <huawei.libin@...wei.com>, <wangnan0@...wei.com>,
        <linux-kernel@...r.kernel.org>, Li Bin <huawei.libin@...wei.com>,
        "Xiexiuqi (Xie XiuQi)" <xiexiuqi@...wei.com>,
        "chengjian (D)" <cj.chengjian@...wei.com>
Subject: Re: [PATCH v3] perf/trace : Fix repetitious traces of perf on
 tracepoint

Hi, Milian


On 2018/1/16 22:33, Milian Wolff wrote:
>> 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.
>>
>>
the sched_stat_* tracepoint also specify a target process, so it will be 
reported
nrcpus times too.

for example sched_stat_sleep

          swapper     0 [002]   188.752870: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1051 delay=2133649486 [ns]
| |
| |
current task



> 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
>
when current != task.

     #echo 1 > /proc/sys/kernel/sched_schedstats
     #./perf-bin/perf record -e sched:sched_stat_sleep ./test_fork_loop

before this patch:
            :1050  1050 [000]   186.597339: sched:sched_stat_sleep: 
comm=perf pid=1051 delay=22955314 [ns]
           :1050  1050 [000]   186.597397: sched:sched_stat_sleep: 
comm=perf pid=1051 delay=22955314 [ns]
            :1050  1050 [000]   186.597406: sched:sched_stat_sleep: 
comm=perf pid=1051 delay=22955314 [ns]
            :1050  1050 [000]   186.597415: sched:sched_stat_sleep: 
comm=perf pid=1051 delay=22955314 [ns]
          swapper     0 [002]   188.752870: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1051 delay=2133649486 [ns]
          swapper     0 [002]   188.752899: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1051 delay=2133649486 [ns]
          swapper     0 [002]   188.752952: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1051 delay=2133649486 [ns]
          swapper     0 [002]   188.752965: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1051 delay=2133649486 [ns]

after this patch:
            :1041  1041 [001]    62.447062: sched:sched_stat_sleep: 
comm=perf pid=1042 delay=43035826 [ns]
          swapper     0 [001]    62.704644: sched:sched_stat_sleep: 
comm=bug_fork_loop pid=1042 delay=234613068 [ns]


>
> 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?
>
  Yeah, this patch fix it.

Thanks.
     CHENG Jian