linux-kernel - Re: [PATCH 1/1] perf/x86/intel: Add perf core PMU support for Intel Knights Landing

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Date:	Wed, 9 Dec 2015 15:22:29 -0800
From:	Harish Chegondi <harish.chegondi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	Harish Chegondi <harish.chegondi@...il.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Kan Liang <kan.liang@...el.com>,
	Lukasz Anaczkowski <lukasz.anaczkowski@...el.com>
Subject: Re: [PATCH 1/1] perf/x86/intel: Add perf core PMU support for Intel
 Knights Landing



On 12/08/2015 12:37 AM, Peter Zijlstra wrote:
> On Mon, Dec 07, 2015 at 02:28:18PM -0800, Harish Chegondi wrote:
>> Knights Landing core is based on Silvermont core with several differences.
>> Like Silvermont, Knights Landing has 8 pairs of LBR MSRs. However, the
>> LBR MSRs addresses match those of the Xeon cores' first 8 pairs of LBR MSRs
>
>> +/* Knights Landing */
>> +void intel_pmu_lbr_init_knl(void)
>> +{
>> +	x86_pmu.lbr_nr	   = 8;
>> +	x86_pmu.lbr_tos    = MSR_LBR_TOS;
>> +	x86_pmu.lbr_from   = MSR_LBR_NHM_FROM;
>> +	x86_pmu.lbr_to     = MSR_LBR_NHM_TO;
>> +
>> +	x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
>> +	x86_pmu.lbr_sel_map  = snb_lbr_sel_map;
> Also, unlike Silvermont, this thing seems to have hardware LBR filters.
> So would it not be more accurate to say the KNL has a big core LBR
> instead? (Note that this LBR setup isn't specific to Xeon's, all of the
> Core chips have this, including the client parts).
We cannot say that KNL has a big core LBR. This is because architectural MSR IA32_PERF_CAPABILITIES[5:0] which indicates the format of the address that is stored in the LBR stack is different for KNL (IA32_PERF_CAPABILITIES[5:0] = 0x1) and big core (for example, Haswell IA32_PERF_CAPABILITIES[5:0]=0x4). Haswell LBR stack has TSX info which KNL LBR stack doesn't have.

Thanks for the review!

>
>> +	pr_cont("8-deep LBR, ");
>> +}
> .
>


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