linux-kernel - Re: [PATCH v3] perf sched: Fix sched latency analysis incorrect

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Date:   Mon, 27 Mar 2023 12:00:52 -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 v3] perf sched: Fix sched latency analysis incorrect

On Thu, Mar 16, 2023 at 11:33 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.

Have you checked perf sched replay (add_sched_event_wakeup)?  I think
it'd make unnecessary sched atoms for sched_wakeup.

Can we check the wakeup and waking events and disable the wakeup
if the waking is found like in perf_sched__timehist?

Thanks,
Namhyung


>
> I used 'perf record -e "sched:* "' to record both wakeup and waking events,
> and use fixed perf version to analysis them, the result is correct.
> Because the function "latency_wakeup_event" will change atom->state to
> THREAD_WAIT_CPU at waking event, and judge the 'atom->state !=
> THREAD_SLEEPING' is false then returned at wakeup event.
>
> Signed-off-by: Chunxin Zang <zangchunxin@...iang.com>
> Signed-off-by: Jerry Zhou <zhouchunhua@...iang.com>
> ---
>
>         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 | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 86e18575c9be..1af4ec1ac824 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -1819,6 +1819,7 @@ static int perf_sched__read_events(struct perf_sched *sched)
>         const struct evsel_str_handler handlers[] = {
>                 { "sched:sched_switch",       process_sched_switch_event, },
>                 { "sched:sched_stat_runtime", process_sched_runtime_event, },
> +               { "sched:sched_waking",       process_sched_wakeup_event, },
>                 { "sched:sched_wakeup",       process_sched_wakeup_event, },
>                 { "sched:sched_wakeup_new",   process_sched_wakeup_event, },
>                 { "sched:sched_migrate_task", process_sched_migrate_task_event, },
> --
> 2.25.1
>
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