linux-kernel - Re: [RFC/PATCH] perf sched: Implement 'perf sched runtime' command

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Date:	Tue, 25 Aug 2015 17:07:06 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCH] perf sched: Implement 'perf sched runtime' command

Hi David,

On Mon, Aug 24, 2015 at 11:19:44PM -0700, David Ahern wrote:
> On 8/24/15 11:11 PM, Namhyung Kim wrote:
> >
> >+static int perf_sched__read_runtime_events(struct perf_sched *sched)
> >+{
> >+	const struct perf_evsel_str_handler handlers[] = {
> >+		{ "sched:sched_switch",	      process_sched_switch_event, },
> >+		{ "sched:sched_stat_runtime", process_sched_runtime_event, },
> >+		{ "sched:sched_stat_sleep",   process_sched_sleep_event, },
> >+		{ "sched:sched_stat_wait",    process_sched_wait_event, },
> >+		{ "sched:sched_stat_iowait",  process_sched_iowait_event, },
> >+		{ "sched:sched_migrate_task", process_sched_migrate_task_event, },
> >+	};
> 
> I like the concept (obviously since I have invested so much time in other
> solutions). But... you cannot rely on the sched_stat tracepoints being
> enabled. I believe it is a performance hit to have CONFIG_SCHEDSTATS enabled
> and distributions (e.g., Fedora) do not have it enabled.

Yes, I know that some distributions don't enable SCHEDSTATS.  But as
perf sched record already requires it, I think it's ok to use those
events in other sched commands.

Maybe we could fix 'perf sched record' not to requires SCHEDSTATS.
All commands in perf sched just use stat_runtime event currently.  And
I guess we can calculate/approximate the stat times using sched_switch
events (and wakeup events) only.  But it also requires changing other
sched commands not to use sched_stat_runtime.

Thanks,
Namhyung
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