linux-kernel - Re: [PATCH] perf_events: fix read() bogus counts when in error state

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Message-ID: <bd4cb8900911260948j6fd743c1u26343073fd1abc46@mail.gmail.com>
Date:	Thu, 26 Nov 2009 18:48:43 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	perfmon2-devel@...ts.sourceforge.net, eranian@...il.com
Subject: Re: [PATCH] perf_events: fix read() bogus counts when in error state

On Thu, Nov 26, 2009 at 6:36 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2009-11-26 at 09:24 -0800, Stephane Eranian wrote:
>>       When a pinned group cannot be scheduled it goes into error state.
>>       Normally a group cannot go out of error state without being explicitly
>>       re-enabled or disabled. There was a bug in per-thread mode, whereby
>>       upon termination of the thread, the group would transition from error
>>       to off leading to bogus counts and timing information returned by
>>       read().
>
>>       Signed-off-by: Stephane Eranian <eranian@...gle.com>
>
> Right, good catch, totally forgot about error state :/
>
You need to clarify what pin actually means for per-thread
and I'd like to see an explanation for what happens when
sampling.
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