linux-kernel - Re: [PATCH] perf record: Fix synthesis failure warnings

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Date:   Thu, 8 Sep 2022 15:58:18 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Olsa <jolsa@...hat.com>, Ian Rogers <irogers@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf record: Fix synthesis failure warnings

Em Wed, Sep 07, 2022 at 10:58:58AM -0700, Namhyung Kim escreveu:
> On Wed, Sep 7, 2022 at 9:25 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
> >
> > Some calls to synthesis functions set err < 0 but only warn about the
> > failure and continue.  However they do not set err back to zero, relying
> > on subsequent code to do that.
> >
> > That changed with the introduction of option --synth. When --synth=no
> > subsequent functions that set err back to zero are not called.
> >
> > Fix by setting err = 0 in those cases.
> >
> > Example:
> >
> >  Before:
> >
> >    $ perf record --no-bpf-event --synth=all -o /tmp/huh uname
> >    Couldn't synthesize bpf events.
> >    Linux
> >    [ perf record: Woken up 1 times to write data ]
> >    [ perf record: Captured and wrote 0.014 MB /tmp/huh (7 samples) ]
> >    $ perf record --no-bpf-event --synth=no -o /tmp/huh uname
> >    Couldn't synthesize bpf events.
> >
> >  After:
> >
> >    $ perf record --no-bpf-event --synth=no -o /tmp/huh uname
> >    Couldn't synthesize bpf events.
> >    Linux
> >    [ perf record: Woken up 1 times to write data ]
> >    [ perf record: Captured and wrote 0.014 MB /tmp/huh (7 samples) ]
> >
> > Fixes: 41b740b6e8a9 ("perf record: Add --synth option")
> > Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> 
> Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks, applied.

- Arnaldo

 
> Thanks,
> Namhyung
> 
> 
> > ---
> >  tools/perf/builtin-record.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index bce8c941d558..7713246a393f 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -1974,14 +1974,18 @@ static int record__synthesize(struct record *rec, bool tail)
> >
> >         err = perf_event__synthesize_bpf_events(session, process_synthesized_event,
> >                                                 machine, opts);
> > -       if (err < 0)
> > +       if (err < 0) {
> >                 pr_warning("Couldn't synthesize bpf events.\n");
> > +               err = 0;
> > +       }
> >
> >         if (rec->opts.synth & PERF_SYNTH_CGROUP) {
> >                 err = perf_event__synthesize_cgroups(tool, process_synthesized_event,
> >                                                      machine);
> > -               if (err < 0)
> > +               if (err < 0) {
> >                         pr_warning("Couldn't synthesize cgroup events.\n");
> > +                       err = 0;
> > +               }
> >         }
> >
> >         if (rec->opts.nr_threads_synthesize > 1) {
> > --
> > 2.25.1
> >

-- 

- Arnaldo