linux-kernel - Re: [BUG] perf_events: PERF_FORMAT_GROUP not working correctly when monitoring another task

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Date:	Thu, 06 May 2010 22:22:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Carl Love <carll@...ibm.com>,
	Maynard Johnson <mpjohn@...ibm.com>,
	stephane eranian <eranian@...glemail.com>
Subject: Re: [BUG] perf_events: PERF_FORMAT_GROUP not working correctly
 when monitoring another task

On Thu, 2010-05-06 at 13:09 -0700, Corey Ashford wrote:
> The patch works with the test case I provided, but for some reason it 
> breaks the normal operation of the libpfm4 "task" utility.  If I put 
> more than one event in a group, I get zero counts on all but the first 
> event.  That's even if I don't use the PERF_FORMAT_GROUP option.

Bugger,.. weird though, I can't see how it would affect the state before
the counters get detached from their context (exit() / close()).

> So something appears to be messed up.  I will see if I can construct an 
> arch-independent test case which demonstrates the problem.

That would be awesome, thanks!


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