linux-kernel - Re: [PATCH v4] perf sched: Fix sched latency analysis incorrect

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Date:   Wed, 29 Mar 2023 16:26:38 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Chunxin Zang <zangchunxin@...iang.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, irogers@...gle.com,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jerry Zhou <zhouchunhua@...iang.com>
Subject: Re: [PATCH v4] perf sched: Fix sched latency analysis incorrect

Hello,

On Mon, Mar 27, 2023 at 11:01 PM Chunxin Zang <zangchunxin@...iang.com> wrote:
>
> 'perf sched latency' is incorrect to get process schedule latency
> when it used 'sched:sched_wakeup' to analysis perf.data.
>
> Because 'perf record' prefer use 'sched:sched_waking' to
> 'sched:sched_wakeup' since commit d566a9c2d482 ("perf sched: Prefer
> sched_waking event when it exists"). It's very reasonable to
> evaluate process schedule latency.
>
> Similarly, update sched latency/map/replay to use sched_waking events.
>
> Signed-off-by: Chunxin Zang <zangchunxin@...iang.com>
> Signed-off-by: Jerry Zhou <zhouchunhua@...iang.com>

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

Thanks,
Namhyung


> ---
>
>         changelogs in v4:
>         1) disable to process wakeup event if wakingup event is found.
>
>         changelogs in v3:
>         1) fix non-ASCII characters in commit log.
>
>         changelogs in v2:
>         1) fix email address disappearing in 'signed off by'
>
>  tools/perf/builtin-sched.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 86e18575c9be..ec443df8e05c 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -1516,6 +1516,14 @@ static int process_sched_wakeup_event(struct perf_tool *tool,
>         return 0;
>  }
>
> +static int process_sched_wakeup_ignore(struct perf_tool *tool __maybe_unused,
> +                                     struct evsel *evsel __maybe_unused,
> +                                     struct perf_sample *sample __maybe_unused,
> +                                     struct machine *machine __maybe_unused)
> +{
> +       return 0;
> +}
> +
>  union map_priv {
>         void    *ptr;
>         bool     color;
> @@ -1816,10 +1824,11 @@ static int perf_sched__process_comm(struct perf_tool *tool __maybe_unused,
>
>  static int perf_sched__read_events(struct perf_sched *sched)
>  {
> -       const struct evsel_str_handler handlers[] = {
> +       struct evsel_str_handler handlers[] = {
>                 { "sched:sched_switch",       process_sched_switch_event, },
>                 { "sched:sched_stat_runtime", process_sched_runtime_event, },
>                 { "sched:sched_wakeup",       process_sched_wakeup_event, },
> +               { "sched:sched_waking",       process_sched_wakeup_event, },
>                 { "sched:sched_wakeup_new",   process_sched_wakeup_event, },
>                 { "sched:sched_migrate_task", process_sched_migrate_task_event, },
>         };
> @@ -1839,6 +1848,10 @@ static int perf_sched__read_events(struct perf_sched *sched)
>
>         symbol__init(&session->header.env);
>
> +       /* prefer sched_waking if it is captured */
> +       if (evlist__find_tracepoint_by_name(session->evlist, "sched:sched_waking"))
> +               handlers[2].handler = process_sched_wakeup_ignore;
> +
>         if (perf_session__set_tracepoints_handlers(session, handlers))
>                 goto out_delete;
>
> --
> 2.25.1
>
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