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Subject: Re: [PATCH] perf record: Fix continue profiling after draining the
 buffer
To:     Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>
CC:     <amistry@google.com>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.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>
References: <20210205065001.23252-1-yangjihong1@huawei.com>
 <CAM9d7cgGGWtTkReghATVmMnOd=0dBrghBLgEc9AqT_PF-UP1Rg@mail.gmail.com>
 <YB0h9Gj5lpcuqndo@krava>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <f3b56856-6ede-6f48-fd0a-60614070302f@huawei.com>
Date:   Sun, 7 Feb 2021 08:56:41 +0800
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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
>>>
>>
> 
> .
>