Messages in this thread | | | Date | Wed, 8 May 2019 11:34:21 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] perf/x86/intel: Support PEBS output to PT |
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On Thu, May 02, 2019 at 01:50:22PM +0300, Alexander Shishkin wrote:
> The output setting is per-CPU, so all PEBS events must be either writing > to PT or to the DS area, so in order to not mess up the event scheduling, > we fall back to the latter in case both types of events are scheduled in.
> +static void intel_pmu_pebs_via_pt_disable(struct perf_event *event) > +{ > + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > + > + if (!(event->hw.flags & PERF_X86_EVENT_PEBS_VIA_PT)) > + return; > + > + if (!(cpuc->pebs_enabled & ~PEBS_VIA_PT_MASK)) > + cpuc->pebs_enabled &= ~PEBS_VIA_PT_MASK; > +} > + > +static void intel_pmu_pebs_via_pt_enable(struct perf_event *event) > +{ > + struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > + struct hw_perf_event *hwc = &event->hw; > + struct debug_store *ds = cpuc->ds; > + > + if (!(event->hw.flags & PERF_X86_EVENT_PEBS_VIA_PT)) > + return; > + > + /* > + * In case there's a mix of PEBS->PT and PEBS->DS, fall back > + * to DS. > + */ > + if (cpuc->n_pebs != cpuc->n_pebs_via_pt) { > + /* PEBS-to-DS events present, fall back to DS */ > + intel_pmu_pebs_via_pt_disable(event); > + return; > + } > + > + if (!(event->hw.flags & PERF_X86_EVENT_LARGE_PEBS)) > + cpuc->pebs_enabled |= PEBS_PMI_AFTER_EACH_RECORD; > + > + cpuc->pebs_enabled |= PEBS_OUTPUT_PT; > + > + wrmsrl(MSR_RELOAD_PMC0 + hwc->idx, ds->pebs_event_reset[hwc->idx]); > +} > + > void intel_pmu_pebs_enable(struct perf_event *event) > { > struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > @@ -1100,6 +1146,8 @@ void intel_pmu_pebs_enable(struct perf_event *event) > } else { > ds->pebs_event_reset[hwc->idx] = 0; > } > + > + intel_pmu_pebs_via_pt_enable(event); > }
I think that doesn't even do what it says on the tin. Suppose you first schedule that PEBS-via-PT event and then the normal one, nothing then cancels the PT link.
Like I wrote in that prevoius email; I really don't like this. I think silently falling back to another output method is wrong.
Ideally we create schedulig conflicts and cause the PT and DS events to round robin.
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