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SubjectRe: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics
On Tue, May 28, 2019 at 02:56:15PM +0200, Peter Zijlstra wrote:
> On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@linux.intel.com wrote:
>
> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > index e9075d57853d..07ecfe75f0e6 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -91,16 +91,20 @@ u64 x86_perf_event_update(struct perf_event *event)
> > new_raw_count) != prev_raw_count)
> > goto again;

AFAICT, you don't actually need that cmpxchg loop for the metric crud.

> >
> > - /*
> > - * Now we have the new raw value and have updated the prev
> > - * timestamp already. We can now calculate the elapsed delta
> > - * (event-)time and add that to the generic event.
> > - *
> > - * Careful, not all hw sign-extends above the physical width
> > - * of the count.
> > - */
> > - delta = (new_raw_count << shift) - (prev_raw_count << shift);
> > - delta >>= shift;
> > + if (unlikely(hwc->flags & PERF_X86_EVENT_UPDATE))
> > + delta = x86_pmu.metric_update_event(event, new_raw_count);
> > + else {
> > + /*
> > + * Now we have the new raw value and have updated the prev
> > + * timestamp already. We can now calculate the elapsed delta
> > + * (event-)time and add that to the generic event.
> > + *
> > + * Careful, not all hw sign-extends above the physical width
> > + * of the count.
> > + */
> > + delta = (new_raw_count << shift) - (prev_raw_count << shift);
> > + delta >>= shift;
> > + }
> >
> > local64_add(delta, &event->count);
> > local64_sub(delta, &hwc->period_left);
>
> > @@ -1186,6 +1194,9 @@ int x86_perf_event_set_period(struct perf_event *event)
> > if (idx == INTEL_PMC_IDX_FIXED_BTS)
> > return 0;
> >
> > + if (x86_pmu.set_period && x86_pmu.set_period(event))
> > + goto update_userpage;
> > +
> > /*
> > * If we are way outside a reasonable range then just skip forward:
> > */
> > @@ -1234,6 +1245,7 @@ int x86_perf_event_set_period(struct perf_event *event)
> > (u64)(-left) & x86_pmu.cntval_mask);
> > }
> >
> > +update_userpage:
> > perf_event_update_userpage(event);
> >
> > return ret;
>
>
> *groan*.... that's pretty terrible.

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