linux-kernel - Re: [PATCH 2/3] perf tools: Record sampling time for each entry

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Message-ID: <1385996264.1710.26.camel@leonhard>
Date:	Mon, 02 Dec 2013 23:57:44 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Pekka Enberg <penberg@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 2/3] perf tools: Record sampling time for each entry

2013-12-02 (월), 09:39 -0300, Arnaldo Carvalho de Melo:
> Em Mon, Dec 02, 2013 at 03:53:18PM +0900, Namhyung Kim escreveu:
> > From: Namhyung Kim <namhyung.kim@....com>
> > 
> > Calculate elapsed time for each sample and record it.  The elapsed
> > time is a diff between current sample->time and previous sample->time
> > which was saved for each evsel and cpu.
> 
> Can you elaborate on why this is interesting to have? What meaning can
> one get from the sample->time - prev_sample->time?
> 
> We need clearer changelogs...

Sorry about that.. how about this?

Sometimes users might want see a relation between value and time of a
sample.  And the time itself is a very important information to have.
As the sample->period value is a diff of counter values between samples
it might make sense to add time-diff between samples into a hist entry.

To do that, calculate elapsed time for each sample and record it.  The
elapsed time is the diff between current sample->time and previous
sample->time which was saved for each evsel.

Thanks,
Namhyung


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