linux-kernel - Re: [BUG] perf stat: hangs with -p and process completes

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Date:   Tue, 16 Oct 2018 11:10:12 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [BUG] perf stat: hangs with -p and process completes

Jiri,

Thanks for looking into this.
Yeah, I don't think you need a kernel patch to make this work.
You can poll in the app.
Let me try this out.


On Tue, Oct 16, 2018 at 9:25 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Tue, Oct 16, 2018 at 01:03:41PM +0200, Jiri Olsa wrote:
> > On Fri, Oct 12, 2018 at 02:26:09PM -0700, Stephane Eranian wrote:
> > > Hi,
> > >
> > > I am running into a perf stat issue with the -p option which allows you
> > > to attach to a running process. If that process happens to terminate
> > > while under monitoring
> > > perf hangs in there and never terminates. The proper behavior would be to stop.
> > > I can see the issue in that the attached process is not a child, so
> > > wait() would not work.
> > >
> > > To reproduce:
> > >   $ sleep 10 &
> > >   $ perf stat -p $!
> > >
> > > doing the same with perf record works, so there is a solution to this problem.
> >
> > yea, we don't poll for the event state change in perf stat,
> > but we do that in perf record.. also because the perf poll
> > code in kernel is originaly meant for tracking the ring
> > buffer state
> >
> > maybe we could return EPOLLIN for alive events without ring
> > buffer.. like below (totaly untested) and add polling for
> > event state into perf stat
> >
> > cc-ing perf folks
> >
>
> on the second thought attached patch works as well
> without kernel change
>
> jirka
>
>
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index b86aba1c8028..d1028d7755bb 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -409,6 +409,28 @@ static struct perf_evsel *perf_evsel__reset_weak_group(struct perf_evsel *evsel)
>         return leader;
>  }
>
> +static bool is_target_alive(struct target *_target,
> +                           struct thread_map *threads)
> +{
> +       struct stat st;
> +       int i;
> +
> +       if (!target__has_task(_target))
> +               return true;
> +
> +       for (i = 0; i < threads->nr; i++) {
> +               char path[PATH_MAX];
> +
> +               scnprintf(path, PATH_MAX, "%s/%d", procfs__mountpoint(),
> +                         threads->map[i].pid);
> +
> +               if (!stat(path, &st))
> +                       return true;
> +       }
> +
> +       return false;
> +}
> +
>  static int __run_perf_stat(int argc, const char **argv, int run_idx)
>  {
>         int interval = stat_config.interval;
> @@ -579,6 +601,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>                 enable_counters();
>                 while (!done) {
>                         nanosleep(&ts, NULL);
> +                       if (!is_target_alive(&target, evsel_list->threads))
> +                               break;
>                         if (timeout)
>                                 break;
>                         if (interval) {