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Date: Thu, 10 Dec 2015 00:37:27 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Harish Chegondi <harish.chegondi@intel.com>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
        Harish Chegondi <harish.chegondi@gmail.com>,
        Andi Kleen <andi.kleen@intel.com>, Kan Liang <kan.liang@intel.com>,
        Lukasz Anaczkowski <lukasz.anaczkowski@intel.com>
Subject: Re: [PATCH 1/1] perf/x86/intel: Add perf core PMU support for Intel
 Knights Landing
Message-ID: <20151209233727.GS6356@twins.programming.kicks-ass.net>
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 <5668B7B4.9070102@intel.com>
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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.