linux-kernel - Re: [PATCH] perf stat: Pass PERF_STAT_RUN environment variable for each run

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Message-ID: <20140717084011.GG19379@twins.programming.kicks-ass.net>
Date:	Thu, 17 Jul 2014 10:40:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>, Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH] perf stat: Pass PERF_STAT_RUN environment variable for
 each run

On Thu, Jul 17, 2014 at 05:31:14PM +0900, Namhyung Kim wrote:
> Hi Peter,
> 
> On Thu, Jul 17, 2014 at 5:26 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Thu, Jul 17, 2014 at 05:21:06PM +0900, Namhyung Kim wrote:
> >> When perf stat runs multiple times via -r option, it's sometimes
> >> useful for a workload to know which run it executing.  So pass new
> >> PERF_STAT_RUN environment variable to the workload for each run
> >> (starting from 1).
> >
> > This seems counter intuitive, runs should be _identical_ otherwise
> > there's no point. That means the workload should very much _not_ know
> > these things.
> 
> But I think it can be useful if a workload wants to save logfiles
> based on the iteration number for example.  If it doesn't want, it can
> just ignore. :)

That's the wrong way around. Also, there's --pre and --post hooks to
preserve logfiles if you really have to do that kind of thing.



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