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SubjectRe: [PATCH v2] Poll for monitored tasks being alive in fork mode
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Hi Arnaldo,

Is this patch acceptable?

Thanks
Jin Yao

On 1/7/2019 5:05 PM, Jiri Olsa wrote:
> On Mon, Jan 07, 2019 at 09:00:50AM +0800, Jin Yao wrote:
>> Following test shows the stat keeps running even if no longer
>> task to monitor (mgen exits at ~5s).
>>
>> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10
>> time counts unit events
>> 1.000148916 1,308,365,864 cycles
>> 2.000379171 1,297,269,875 cycles
>> 3.000556719 1,297,187,078 cycles
>> 4.000914241 761,261,827 cycles
>> 5.001306091 <not counted> cycles
>> 6.001676881 <not counted> cycles
>> 7.002046336 <not counted> cycles
>> 8.002405651 <not counted> cycles
>> 9.002766625 <not counted> cycles
>> 10.001395827 <not counted> cycles
>>
>> We'd better finish stat immediately if there's no longer task to
>> monitor.
>>
>> After:
>>
>> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10
>> time counts unit events
>> 1.000180062 1,236,592,661 cycles
>> 2.000421539 1,223,733,572 cycles
>> 3.000609910 1,297,047,663 cycles
>> 4.000807545 1,297,215,816 cycles
>> 5.001001578 1,297,208,032 cycles
>> 6.001390345 582,343,659 cycles
>> sleep: Terminated
>>
>> Now the stat exits immediately when the monitored tasks ends.
>>
>> v2:
>> ---
>> There is a potential race condition window, that is the
>> child_pid set with -1 and kill(-1, SIGTERM) may happen.
>> Jiri provides a simple method which stores the child_pid to
>> a local variable and check the local variable before kill().
>> At least, we can avoid the kill(-1, SIGTERM) case.
>>
>> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
>
> Reviewed-by: Jiri Olsa <jolsa@kernel.org>
>
> thanks,
> jirka
>
>> ---
>> tools/perf/builtin-stat.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
>> index 63a3afc..bd5fb8e 100644
>> --- a/tools/perf/builtin-stat.c
>> +++ b/tools/perf/builtin-stat.c
>> @@ -553,6 +553,15 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>>
>> if (interval || timeout) {
>> while (!waitpid(child_pid, &status, WNOHANG)) {
>> + if (!is_target_alive(&target,
>> + evsel_list->threads)) {
>> + int pid = child_pid;
>> +
>> + if (pid != -1)
>> + kill(pid, SIGTERM);
>> + break;
>> + }
>> +
>> nanosleep(&ts, NULL);
>> if (timeout)
>> break;
>> --
>> 2.7.4
>>

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