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Subject: Re: [PATCH] perf record: Fix continue profiling after draining the
 buffer
To:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>
CC:     Namhyung Kim <namhyung@kernel.org>, <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>,
        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> <YC5ptbU8Mavb1a/t@kernel.org>
 <YC6fVHohih5giNf7@kernel.org>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <5a76a82e-7ec1-d510-309e-a38a1b41027e@huawei.com>
Date:   Mon, 22 Feb 2021 09:31:51 +0800
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Hello,

On 2021/2/19 1:09, Arnaldo Carvalho de Melo wrote:
> Em Thu, Feb 18, 2021 at 10:20:53AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Fri, Feb 05, 2021 at 11:46:12AM +0100, Jiri Olsa escreveu:
>>> 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
>>
>> Yes, this can't work on systems without eventfd, it will simply not
>> build, and why do we have to make the definition of this function
>> conditional on HAVE_EVENTFD_SUPPORT?
>>
>> I'm missing something :-\
>>
>> Yeah, this whole call to evlist__add_pollfd is already surrounded by
>> #ifdef HAVE_EVENTFD_SUPPORT:
>>
>> 1656         if (zstd_init(&session->zstd_data, rec->opts.comp_level) < 0) {
>> 1657                 pr_err("Compression initialization failed.\n");
>> 1658                 return -1;
>> 1659         }
>> 1660 #ifdef HAVE_EVENTFD_SUPPORT
>> 1661         done_fd = eventfd(0, EFD_NONBLOCK);
>> 1662         if (done_fd < 0) {
>> 1663                 pr_err("Failed to create wakeup eventfd, error: %m\n");
>> 1664                 status = -1;
>> 1665                 goto out_delete_session;
>> 1666         }
>> 1667         err = evlist__add_pollfd(rec->evlist, done_fd);
>> 1668         if (err < 0) {
>> 1669                 pr_err("Failed to add wakeup eventfd to poll list\n");
>> 1670                 status = err;
>> 1671                 goto out_delete_session;
>> 1672         }
>> 1673 #endif // HAVE_EVENTFD_SUPPORT
>> 1674
>> 1675         session->header.env.comp_type  = PERF_COMP_ZSTD;
>> 1676         session->header.env.comp_level = rec->opts.comp_level;
>>
>> Jiri, does your Acked-by stands? Namhyung?
> 
> Thanks tested and applied, together with Jiri's Tested-by,
> 
> - Arnaldo
> .
> 
Is this patch okay? Is there anything that needs to be modified?

Thanks,
Yang