Re: [PATCH v2] Poll for monitored tasks being alive in fork mode

[Jin, Yao]

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@xxxxxxxxxxxxxxx>
>
> Reviewed-by: Jiri Olsa <jolsa@xxxxxxxxxx>
>
> 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