linux-kernel - Re: [PATCH] perf record: Fix wrong comm in system-wide mode with delay

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Date:   Mon, 30 Aug 2021 10:33:16 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf record: Fix wrong comm in system-wide mode with delay

On Fri, Aug 27, 2021 at 4:32 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Stephane found that the name of the forked process in a system-wide
> mode is wrong when --delay option is used.  For example,
>
>   # perf record -a --delay=1000  noploop 3
>
> The noploop process will run a busy loop for 3 second.  And on an idle
> machine it should show up at the top in the perf report.  It works
> well without the --delay option.  But if I add the option, it showed
> 'perf' not 'noploop'.
>
>   # perf report -s comm -q | head -3
>       52.94%  perf
>       16.65%  swapper
>       12.04%  chrome
>
> It turned out that the dummy event didn't work at all and it missed
> COMM and MMAP events for the noploop process (and others too).  We
> should enable the dummy event immediately in system-wide mode, as the
> enable-on-exec would work only for task events.
>
> With this change,
>
>   # perf report -s comm -q | head -3
>       52.75%  noploop
>       17.03%  swapper
>       12.83%  chrome
>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Reported-by: Stephane Eranian <eranian@...gle.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/builtin-record.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 548c1dbde6c5..acfe66e31cf0 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -910,7 +910,8 @@ static int record__open(struct record *rec)
>                  * Enable the dummy event when the process is forked for
>                  * initial_delay, immediately for system wide.
>                  */
> -               if (opts->initial_delay && !pos->immediate)
> +               if (opts->initial_delay && !pos->immediate &&
> +                   !target__has_cpu(&opts->target))
>                         pos->core.attr.enable_on_exec = 1;
>                 else
>                         pos->immediate = 1;
> --
> 2.33.0.259.gc128427fd7-goog
>