linux-kernel - Re: [PATCH 4/5] perf, x86: Support full width counting

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Date:	Tue, 5 Feb 2013 20:09:02 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/5] perf, x86: Support full width counting

On Tue, Feb 05, 2013 at 04:15:26PM +0100, Stephane Eranian wrote:
> > --- a/arch/x86/kernel/cpu/perf_event_intel.c
> > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> > @@ -2228,5 +2228,11 @@ __init int intel_pmu_init(void)
> >                 }
> >         }
> >
> > +       /* Support full width counters using alternative MSR range */
> > +       if (x86_pmu.intel_cap.fw_write) {
> > +               x86_pmu.max_period = x86_pmu.cntval_mask;
> 
> Something is not clear to me: What happens to the fixed counters with
> full writes? Were they already full-width? The SDM does not explain what
> happens to them with this extension. Could you clarify?

I tested and they always support the full reported width.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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