linux-kernel - Re: perf_counter Atom patch

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Date:	Tue, 23 Jun 2009 16:53:21 +0800
From:	Yong Wang <yong.y.wang@...ux.intel.com>
To:	eranian@...il.com
Cc:	Yong Wang <yong.y.wang@...ux.intel.com>,
	"Wang, Yong Y" <yong.y.wang@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: perf_counter Atom patch

On Tue, Jun 23, 2009 at 10:40:45AM +0200, stephane eranian wrote:
> Yong,
> 
> On Tue, Jun 23, 2009 at 10:27 AM, stephane
> eranian<eranian@...glemail.com> wrote:
> > Hi,
> >
> > On Tue, Jun 23, 2009 at 9:59 AM, Yong Wang<yong.y.wang@...ux.intel.com> wrote:
> >> On Tue, Jun 23, 2009 at 09:45:03AM +0200, stephane eranian wrote:
> >>>
> >>> Unfortunately, I don't have a N270 to compare with your results.
> >>> We need to verify whether or not N270 implements the fixed counters.
> >>> Does it report architected perfmon v3 or v1?
> >>>
> >>
> >> All Atom processors report perfmon v3 as specified in SDM. N270 is no
> >> exception.
> >>
> > V3 does not set a minimal number of fixed counters, could be zero. But
> > that seems
> > odd. Let me ask around.
> >
> Second thought on this:
>        x86_pmu.num_counters_fixed      =
> max((int)edx.split.num_counters_fixed, 3);
> 
>         rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, x86_pmu.intel_ctrl);
> 
> 
> Forcing num_counter_fixed is not enough, you need to make sure they are actually
> activated in GLOBAL_CTRL, i.e., make sure bits 32-34 are set in intel_ctrl.
> Depending on which machine you're on, the power on value for GLOBAL_CTRL
> changes. The correct value for it should be that ONLY generic counters are on
> by default.
> 

Oh, this might be why fixed counter do not work on my Atom box. I will
look into it. BTW, why should ONLY generic counters be on by default?

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