linux-kernel - Re: perf: p6 PMU working by accident, should we fix it and KNC?

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Date:	Fri, 19 Oct 2012 16:07:49 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	eranian@...il.com,
	"Meadows, Lawrence F" <lawrence.f.meadows@...el.com>
Subject: Re: perf: p6 PMU working by accident, should we fix it and KNC?

On Wed, 2012-10-17 at 11:35 -0400, Vince Weaver wrote:
> 
> This is by accident; it looks like the code does 
>    val |= ARCH_PERFMON_EVENTSEL_ENABLE;
> in p6_pmu_disable_event() so that events are never truly disabled
> (is this a bug?  should it be &=~ instead?).  

I think that's on purpose.. from what I can remember p6 only has a
single EN bit (on PMC0) that acts for both counters. So what I did was
treat that as a global enable/disable (which it is) and did the local
enable/disable by using the NOP events.

There really might be bugs in there, its not like I use this class of
hardware very frequently (nor do anybody much it seems).


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