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

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Date:	Tue, 23 Oct 2012 13:28:07 +0800
From:	"Yan, Zheng" <zheng.z.yan@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	linux-kernel@...r.kernel.org, eranian@...gle.com,
	ak@...ux.intel.com
Subject: Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

On 10/22/2012 06:33 PM, 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()?
> 

So far we use the call stack feature only for ring 3. but even for ring 0,
it's OK. because LBR is disabled at the very beginning of PMI hander, and
enabled when exiting the PMI hander. the depth to _intel_pmu_lbr_enable/
_intel_pmu_lbr_disable are the same. So entries that are added by calling
_intel_pmu_lbr_disable will be popped during enabling LBR.

Regards
Yan, Zheng
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