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SubjectRe: [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@redhat.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) {

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