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

[Yang Jihong]

Hello,

On 2021/2/7 8:56, Yang Jihong wrote:
> Hello,
>
> On 2021/2/5 18:46, Jiri Olsa wrote:
> > 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@xxxxxxxxxx> 
> > > 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@xxxxxxxxxx>
> > > > ---
> > > >   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
> I have tested that if "eventfd" feature is removed from the 
> FEATURE_TESTS_BASIC list in Makefile.feature,
> evlist__add_wakeup_eventfd will not be build.
>
> Modify as follows:
>
> diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
> index 97cbfb31b762..d1603050764a 100644
> --- a/tools/build/Makefile.feature
> +++ b/tools/build/Makefile.feature
> @@ -32,7 +32,6 @@ FEATURE_TESTS_BASIC :=                  \
>           backtrace                       \
>           dwarf                           \
>           dwarf_getlocations              \
> -        eventfd                         \
>           fortify-source                  \
>           sync-compare-and-swap           \
>           get_current_dir_name            \
>
> Thanks,
> Yang
>
> > > > +
> > > >   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
> >
> > .
Do have any other questions about this patch?
Look forward to your review.

Thanks,
Yang