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

[Yang Jihong]

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
>
> .