linux-kernel - Re: [PATCH] perf record: Fix continue profiling after draining the buffer

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Message-ID: <YC6fVHohih5giNf7@kernel.org>
Date:   Thu, 18 Feb 2021 14:09:40 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        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>,
        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

Em Thu, Feb 18, 2021 at 10:20:53AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Feb 05, 2021 at 11:46:12AM +0100, Jiri Olsa escreveu:
> > 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
> 
> Yes, this can't work on systems without eventfd, it will simply not
> build, and why do we have to make the definition of this function
> conditional on HAVE_EVENTFD_SUPPORT?
> 
> I'm missing something :-\
> 
> Yeah, this whole call to evlist__add_pollfd is already surrounded by
> #ifdef HAVE_EVENTFD_SUPPORT:
> 
> 1656         if (zstd_init(&session->zstd_data, rec->opts.comp_level) < 0) {
> 1657                 pr_err("Compression initialization failed.\n");
> 1658                 return -1;
> 1659         }
> 1660 #ifdef HAVE_EVENTFD_SUPPORT
> 1661         done_fd = eventfd(0, EFD_NONBLOCK);
> 1662         if (done_fd < 0) {
> 1663                 pr_err("Failed to create wakeup eventfd, error: %m\n");
> 1664                 status = -1;
> 1665                 goto out_delete_session;
> 1666         }
> 1667         err = evlist__add_pollfd(rec->evlist, done_fd);
> 1668         if (err < 0) {
> 1669                 pr_err("Failed to add wakeup eventfd to poll list\n");
> 1670                 status = err;
> 1671                 goto out_delete_session;
> 1672         }
> 1673 #endif // HAVE_EVENTFD_SUPPORT
> 1674 
> 1675         session->header.env.comp_type  = PERF_COMP_ZSTD;
> 1676         session->header.env.comp_level = rec->opts.comp_level;
> 
> Jiri, does your Acked-by stands? Namhyung?

Thanks tested and applied, together with Jiri's Tested-by,

- Arnaldo