linux-kernel - Re: [PATCH 2/2] x86, perf: Use INST_RETIRED.PREC

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Date:	Tue, 1 Dec 2015 14:41:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] x86, perf: Use INST_RETIRED.PREC_DIST for cycles:ppp

On Mon, Nov 30, 2015 at 04:28:09PM -0800, Andi Kleen wrote:
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 9dfbba5..ba41899 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -482,6 +482,9 @@ int x86_pmu_hw_config(struct perf_event *event)
>  			/* Support for IP fixup */
>  			if (x86_pmu.lbr_nr || x86_pmu.intel_cap.pebs_format >= 2)
>  				precise++;
> +
> +			if (x86_pmu.pebs_aliases)
> +				precise++;

This is not accurate, it would allow :ppp for core2 for example, which
does not at all support PREC_DIST events.

Something like so on top?

--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -483,7 +483,7 @@ int x86_pmu_hw_config(struct perf_event
 			if (x86_pmu.lbr_nr || x86_pmu.intel_cap.pebs_format >= 2)
 				precise++;
 
-			if (x86_pmu.pebs_aliases)
+			if (x86_pmu.pebs_prec_dist)
 				precise++;
 		}
 
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -593,7 +593,8 @@ struct x86_pmu {
 			bts_active	:1,
 			pebs		:1,
 			pebs_active	:1,
-			pebs_broken	:1;
+			pebs_broken	:1,
+			pebs_prec_dist	:1;
 	int		pebs_record_size;
 	void		(*drain_pebs)(struct pt_regs *regs);
 	struct event_constraint *pebs_constraints;
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -3470,6 +3470,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.event_constraints = intel_ivb_event_constraints;
 		x86_pmu.pebs_constraints = intel_ivb_pebs_event_constraints;
 		x86_pmu.pebs_aliases = intel_pebs_aliases_ivb;
+		x86_pmu.pebs_prec_dist = true;
 		if (boot_cpu_data.x86_model == 62)
 			x86_pmu.extra_regs = intel_snbep_extra_regs;
 		else
@@ -3503,6 +3504,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.pebs_constraints = intel_hsw_pebs_event_constraints;
 		x86_pmu.extra_regs = intel_snbep_extra_regs;
 		x86_pmu.pebs_aliases = intel_pebs_aliases_ivb;
+		x86_pmu.pebs_prec_dist = true;
 		/* all extra regs are per-cpu when HT is on */
 		x86_pmu.flags |= PMU_FL_HAS_RSP_1;
 		x86_pmu.flags |= PMU_FL_NO_HT_SHARING;
@@ -3538,6 +3540,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.pebs_constraints = intel_hsw_pebs_event_constraints;
 		x86_pmu.extra_regs = intel_snbep_extra_regs;
 		x86_pmu.pebs_aliases = intel_pebs_aliases_ivb;
+		x86_pmu.pebs_prec_dist = true;
 		/* all extra regs are per-cpu when HT is on */
 		x86_pmu.flags |= PMU_FL_HAS_RSP_1;
 		x86_pmu.flags |= PMU_FL_NO_HT_SHARING;
@@ -3560,6 +3563,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.pebs_constraints = intel_skl_pebs_event_constraints;
 		x86_pmu.extra_regs = intel_skl_extra_regs;
 		x86_pmu.pebs_aliases = intel_pebs_aliases_skl;
+		x86_pmu.pebs_prec_dist = true;
 		/* all extra regs are per-cpu when HT is on */
 		x86_pmu.flags |= PMU_FL_HAS_RSP_1;
 		x86_pmu.flags |= PMU_FL_NO_HT_SHARING;
--
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