linux-kernel - Re: [PATCH 02/11] perf: Do not get values from disabled counters in group format read

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Date:	Wed, 24 Oct 2012 14:32:22 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 02/11] perf: Do not get values from disabled counters in
 group format read

On Wed, 2012-10-24 at 14:14 +0200, Jiri Olsa wrote:
> 
> well, x86_pmu_read calls x86_perf_event_update, which expects the
> event
> is active.. if it's not it'll update the count from whatever left in
> event.hw.idx counter.. could be uninitialized or used by others..
> 
Oh right, we shouldn't call ->read() unless ->state ==
PERF_EVENT_STATE_ACTIVE. Aside from that, perf_event_count() should
return the 'right' value regardless state (although excluding ERROR
might make sense).
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