linux-kernel - Re: perf_counter Atom patch

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Message-ID: <20090623094717.GA30634@elte.hu>
Date:	Tue, 23 Jun 2009 11:47:17 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yong Wang <yong.y.wang@...ux.intel.com>
Cc:	eranian@...il.com, "Wang, Yong Y" <yong.y.wang@...el.com>,
	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


* Yong Wang <yong.y.wang@...ux.intel.com> wrote:

> 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. [...]

Thanks - having a different bootup default for the global ctrl 
indeed sounds like a good and plausible explanation - please send a 
patch for that if you've tested it, removing that quirk and adding 
the global-enable ctrl logic.

	Ingo
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