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Date:   Fri, 5 Feb 2021 11:46:12 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Yang Jihong <yangjihong1@...wei.com>, amistry@...gle.com,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        zhangjinhao2@...wei.com
Subject: Re: [PATCH] perf record: Fix continue profiling after draining the
 buffer

On Fri, Feb 05, 2021 at 07:35:22PM +0900, Namhyung Kim wrote:
> Hello,
> 
> On Fri, Feb 5, 2021 at 3:50 PM Yang Jihong <yangjihong1@...wei.com> wrote:
> >
> > commit da231338ec9c098707c8a1e4d8a50e2400e2fe17 uses eventfd to solve rare race
> > where the setting and checking of 'done' which add done_fd to pollfd.
> > When draining buffer, revents of done_fd is 0 and evlist__filter_pollfd
> > function returns a non-zero value.
> > As a result, perf record does not stop profiling.
> >
> > The following simple scenarios can trigger this condition:
> >
> > sleep 10 &
> > perf record -p $!
> >
> > After the sleep process exits, perf record should stop profiling and exit.
> > However, perf record keeps running.
> >
> > If pollfd revents contains only POLLERR or POLLHUP,
> > perf record indicates that buffer is draining and need to stop profiling.
> > Use fdarray_flag__nonfilterable to set done eventfd to nonfilterable objects,
> > so that evlist__filter_pollfd does not filter and check done eventfd.
> >
> > Fixes: da231338ec9c (perf record: Use an eventfd to wakeup when done)
> > Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> > ---
> >  tools/perf/builtin-record.c | 2 +-
> >  tools/perf/util/evlist.c    | 8 ++++++++
> >  tools/perf/util/evlist.h    | 4 ++++
> >  3 files changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index fd3911650612..51e593e896ea 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -1663,7 +1663,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
> >                 status = -1;
> >                 goto out_delete_session;
> >         }
> > -       err = evlist__add_pollfd(rec->evlist, done_fd);
> > +       err = evlist__add_wakeup_eventfd(rec->evlist, done_fd);
> >         if (err < 0) {
> >                 pr_err("Failed to add wakeup eventfd to poll list\n");
> >                 status = err;
> > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> > index 05363a7247c4..fea4c1e8010d 100644
> > --- a/tools/perf/util/evlist.c
> > +++ b/tools/perf/util/evlist.c
> > @@ -572,6 +572,14 @@ int evlist__filter_pollfd(struct evlist *evlist, short revents_and_mask)
> >         return perf_evlist__filter_pollfd(&evlist->core, revents_and_mask);
> >  }
> >
> > +#ifdef HAVE_EVENTFD_SUPPORT
> > +int evlist__add_wakeup_eventfd(struct evlist *evlist, int fd)
> > +{
> > +       return perf_evlist__add_pollfd(&evlist->core, fd, NULL, POLLIN,
> > +                                      fdarray_flag__nonfilterable);
> > +}
> > +#endif
> 
> Does it build when HAVE_EVENTFD_SUPPORT is not defined?

yea, I was wondering the same.. but it's called only from
code within HAVE_EVENTFD_SUPPORT ifdef

jirka

> 
> Thanks,
> Namhyung
> 
> 
> > +
> >  int evlist__poll(struct evlist *evlist, int timeout)
> >  {
> >         return perf_evlist__poll(&evlist->core, timeout);
> > diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> > index 1aae75895dea..6d4d62151bc8 100644
> > --- a/tools/perf/util/evlist.h
> > +++ b/tools/perf/util/evlist.h
> > @@ -142,6 +142,10 @@ struct evsel *evlist__find_tracepoint_by_name(struct evlist *evlist, const char
> >  int evlist__add_pollfd(struct evlist *evlist, int fd);
> >  int evlist__filter_pollfd(struct evlist *evlist, short revents_and_mask);
> >
> > +#ifdef HAVE_EVENTFD_SUPPORT
> > +int evlist__add_wakeup_eventfd(struct evlist *evlist, int fd);
> > +#endif
> > +
> >  int evlist__poll(struct evlist *evlist, int timeout);
> >
> >  struct evsel *evlist__id2evsel(struct evlist *evlist, u64 id);
> > --
> > 2.17.1
> >
> 

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