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    SubjectRe: [PATCH] perf record: Fix continue profiling after draining the buffer
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    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@huawei.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@huawei.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
    >>>
    >>>
    > 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

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