linux-kernel - Re: [PATCH 1/2] perf script: Skip aggregation for stat events

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Date:   Fri, 5 May 2023 16:43:20 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Sandipan Das <sandipan.das@....com>
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com,
        terrelln@...com, ravi.bangoria@....com, ananth.narayan@....com
Subject: Re: [PATCH 1/2] perf script: Skip aggregation for stat events

Hello,

On Fri, May 5, 2023 at 3:03 AM Sandipan Das <sandipan.das@....com> wrote:
>
> The script command does not support aggregation modes by itself although
> that can be achieved using post-processing scripts. Because of this, it
> does not allocate memory for aggregated event values.
>
> Upon running perf stat record, the aggregation mode is set in the perf
> data file. If the mode is AGGR_GLOBAL, the aggregated event values are
> accessed and this leads to a segmentation fault since these were never
> allocated to begin with. Set the mode to AGGR_NONE explicitly to avoid
> this.
>
> E.g.
>
>   $ perf stat record -e cycles true
>   $ perf script
>
> Before:
>   Segmentation fault (core dumped)
>
> After:
>   CPU   THREAD             VAL             ENA             RUN            TIME EVENT
>    -1   231919          162831          362069          362069          935289 cycles:u
>
> Fixes: 8b76a3188b85 ("perf stat: Remove unused perf_counts.aggr field")
> Signed-off-by: Sandipan Das <sandipan.das@....com>
> Cc: stable@...r.kernel.org # v6.2+

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>  tools/perf/builtin-script.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 006f522d0e7f..c57be48d65bb 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -3647,6 +3647,13 @@ static int process_stat_config_event(struct perf_session *session __maybe_unused
>                                      union perf_event *event)
>  {
>         perf_event__read_stat_config(&stat_config, &event->stat_config);
> +
> +       /*
> +        * Aggregation modes are not used since post-processing scripts are
> +        * supposed to take care of such requirements
> +        */
> +       stat_config.aggr_mode = AGGR_NONE;
> +
>         return 0;
>  }
>
> --
> 2.34.1
>