linux-kernel - Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

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Message-ID: <20121022134505.GG2095@tassilo.jf.intel.com>
Date:	Mon, 22 Oct 2012 06:45:05 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>, linux-kernel@...r.kernel.org,
	eranian@...gle.com
Subject: Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

On Mon, Oct 22, 2012 at 12:33:36PM +0200, Peter Zijlstra wrote:
> On Mon, 2012-10-22 at 14:11 +0800, Yan, Zheng wrote:
> > +       /* LBR callstack does not work well with FREEZE_LBRS_ON_PMI */
> > +       if (!cpuc->lbr_sel || !(cpuc->lbr_sel->config & LBR_CALL_STACK))
> > +               debugctl |= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI; 
> 
> How useful it is without this? How many calls between PMI and us getting
> to intel_pmu_lbr_read()?

We use it only for ring 3. For ring 0 we assume frame pointer or
dwarf information.

So the CPL filter acts as the freeze.

-andi

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