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

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Message-ID: <CAM9d7cj=yyfmCRfEVvp7kCHRE8cTEkRFf_unThde2kNoo-x+GA@mail.gmail.com>
Date:   Wed, 7 Sep 2022 10:58:58 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        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

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,
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
>