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

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