Re: [PATCH 2/2] x86, perf: Use INST_RETIRED.PREC_DIST for cycles:ppp

From: Peter Zijlstra
Date: Tue Dec 01 2015 - 08:42:00 EST


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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