linux-kernel - Re: [RFC/PATCH] perf stat: Show sample events stat for a data file

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Date:	Fri, 8 May 2015 16:46:20 +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>, Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [RFC/PATCH] perf stat: Show sample events stat for a data file

On Wed, Apr 29, 2015 at 08:58:22PM +0900, Namhyung Kim wrote:
> > It would be nice if this thing could support 'perf record -s' which
> > enables perf_event_attr::inherit_stat, which in turn results in
> > PERF_RECORD_READ entries after every PERF_RECORD_EXIT which give the
> > total number of events for each recorded task.
> 
> Hmm.. this is one of the areas that I don't understand what's going
> on.  It'd be nice if you can help me understand and possibly improve
> the doc too.
> 
> So the combination of 'perf record -s' and 'perf report -T' should
> show some per-thread counter values, right?  I've found a bug on it.

Right, they should. perf-record -s should give the event count per
monitored thread, which when summed, should match what perf-stat gives
for that workload.

And agreed on the bug, I can see it too.

> Anyway, I don't understand the numbers it shows.

Me neither. I don't quite know why it has 5 cycles columns, we only
measure the one cycles event.

> 
> So the cycles values on 'perf report -T' are a lot more than the value
> of perf stat.  And I have no idea why it shows 5 different cycles for
> each thread.  Could you shed some light on this?

Sadly no, not making sense. But I can confirm this is what it does.

Lemme go poke at this, its weird.
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