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

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Date:	Thu, 10 Dec 2015 00:37:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Harish Chegondi <harish.chegondi@...el.com>
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 Wed, Dec 09, 2015 at 03:22:29PM -0800, Harish Chegondi wrote:

> 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.

Fair enough I suppose. Applied the patch.
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