Messages in this thread | | | Date | Mon, 30 Mar 2015 14:06:07 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V5 1/6] perf, x86: use the PEBS auto reload mechanism when possible |
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On Mon, Feb 23, 2015 at 09:25:51AM -0500, Kan Liang wrote: > +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c > @@ -673,6 +673,8 @@ void intel_pmu_pebs_enable(struct perf_event *event) > struct hw_perf_event *hwc = &event->hw; > > hwc->config &= ~ARCH_PERFMON_EVENTSEL_INT; > + if (!event->attr.freq) > + hwc->flags |= PERF_X86_EVENT_AUTO_RELOAD; > > cpuc->pebs_enabled |= 1ULL << hwc->idx;
Why not in x86_pmu_event_init()? This is not something that will change, ever, right?
> @@ -680,6 +682,12 @@ void intel_pmu_pebs_enable(struct perf_event *event) > cpuc->pebs_enabled |= 1ULL << (hwc->idx + 32); > else if (event->hw.flags & PERF_X86_EVENT_PEBS_ST) > cpuc->pebs_enabled |= 1ULL << 63; > + > + /* Use auto-reload if possible to save a MSR write in the PMI */ > + if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) { > + ds->pebs_event_reset[hwc->idx] = > + (u64)-hwc->sample_period & x86_pmu.cntval_mask; > + } > } > > void intel_pmu_pebs_disable(struct perf_event *event) > @@ -698,6 +706,7 @@ void intel_pmu_pebs_disable(struct perf_event *event) > wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled); > > hwc->config |= ARCH_PERFMON_EVENTSEL_INT; > + hwc->flags &= ~PERF_X86_EVENT_AUTO_RELOAD;
Equally, we should not ever have to clear this. You cannot change attributes after the event is created, if that flag ever gets set, it stays valid.
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