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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Fri, 5 Feb 2021 19:35:22 +0900
Message-ID: <CAM9d7cgGGWtTkReghATVmMnOd=0dBrghBLgEc9AqT_PF-UP1Rg@mail.gmail.com>
Subject: Re: [PATCH] perf record: Fix continue profiling after draining the buffer
To:     Yang Jihong <yangjihong1@huawei.com>
Cc:     amistry@google.com,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        zhangjinhao2@huawei.com
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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?

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
>