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Subject: Re: [PATCH 1/2] perf: Fix the software events state check
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>
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	 <20110309092818.GC25004@elte.hu>  <20110309135252.GB1730@nowhere>
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Date: Wed, 09 Mar 2011 14:55:59 +0100
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On Wed, 2011-03-09 at 14:52 +0100, Frederic Weisbecker wrote:
> 
> It seems that ->stop() / ->start() are called from perf_adjust_period()
> to update the hardware with the new settings of period_left. The events
> are stopped to avoid any race with events triggering with a stale period_left
> in the hardware level when the software one has been updated, I guess.
> 
> So it doesn't seem to fix any existing bug because for ->stop() and ->start()
> are only useful for hardware events right now. But we may call ->stop() and
> ->start() for further purpose later. In fact that paves the way for the event
> exclusion patchset I'm about to post.
> 
> So it should be .39 material. But a confirmation from Peter would be nice. 

Yeah, that sounds about right, I've already queued these patches
for .39.