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Date:   Wed, 3 Mar 2021 13:43:27 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Yang Jihong <yangjihong1@huawei.com>
Cc:     Jiri Olsa <jolsa@redhat.com>, 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
Subject: Re: [PATCH] perf record: Fix continue profiling after draining the
 buffer
Message-ID: <YD+8r/KiCJmnoJ/f@kernel.org>
References: <20210205065001.23252-1-yangjihong1@huawei.com>
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Em Mon, Feb 22, 2021 at 09:31:51AM +0800, Yang Jihong escreveu:
> 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?

It was merged:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/tools/perf/builtin-record.c?id=e16c2ce7c5ed5de881066c1fd10ba5c09af69559

- Arnaldo