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

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Date:	Tue, 03 Dec 2013 13:33:12 +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

Hi Arnaldo,

On Mon, 2 Dec 2013 15:49:05 -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Dec 02, 2013 at 11:57:44PM +0900, Namhyung Kim escreveu:
>> 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.
>
> Much better! Thanks, and please consider adding this to the man page as
> well, in a followup patch.

Okay.

>
> I'll add the above explanation to the patch, that, as I could read seems
> to not have had any nak, right?

Right.  So will you merge this into your tree with new changelog?  I
found that it break build on an old system due to shadowing 'time'
symbol with local one.

I'll send v2 soon with a fix.

Thanks,
Namhyung
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