Subject: Re: perf_counter Atom patch
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Yong Wang <yong.y.wang@linux.intel.com>
Cc: eranian@gmail.com, "Wang, Yong Y" <yong.y.wang@intel.com>,
       Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Paul Mackerras <paulus@samba.org>, Andi Kleen <andi@firstfloor.org>
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Date: Tue, 23 Jun 2009 11:10:05 +0200
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On Tue, 2009-06-23 at 16:34 +0800, Yong Wang wrote:
> > you could simply consider having 0 fixed counters and everything else would work
> > as expected. But there is a catch, unfortunately, in that there is erratum AE49
> > which says that there is only one enable bit to control the two generic counters
> > on Core Duo/Solo.

Ah, that's similar to P6 like machines. The P6 docs say that to disable
a counter you should simply write all zeros (except the EN bit for ctr0)
to the control register (IIRC).

I suppose we could do something similar on these errata cores, make
x86_pmu_disable_counter() write ARCH_PERFMON_EVENTSEL0_ENABLE instead.

Would that work?

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