Re: [PATCH V7 08/14] perf/x86/intel: Generic support for hardware TopDown metrics

[Liang, Kan]

On 7/24/2020 11:27 AM, peterz@xxxxxxxxxxxxx wrote:
> On Fri, Jul 24, 2020 at 03:19:06PM +0200, peterz@xxxxxxxxxxxxx wrote:
> > On Thu, Jul 23, 2020 at 10:11:11AM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> > > @@ -3375,6 +3428,72 @@ static int intel_pmu_hw_config(struct perf_event *event)
> > >   	if (event->attr.type != PERF_TYPE_RAW)
> > >   		return 0;
> > >   
> > > +	/*
> > > +	 * Config Topdown slots and metric events
> > > +	 *
> > > +	 * The slots event on Fixed Counter 3 can support sampling,
> > > +	 * which will be handled normally in x86_perf_event_update().
> > > +	 *
> > > +	 * The metric events don't support sampling.
> > > +	 *
> > > +	 * For counting, topdown slots and metric events will be
> > > +	 * handled specially for event update.
> > > +	 * A flag PERF_X86_EVENT_TOPDOWN is applied for the case.
> > > +	 */
> > > +	if (x86_pmu.intel_cap.perf_metrics && is_topdown_event(event)) {
> > > +		if (is_metric_event(event)) {
> > > +			struct perf_event *leader = event->group_leader;
> > > +			struct perf_event *sibling;
> > > +
> > > +			/* The metric events don't support sampling. */
> > > +			if (is_sampling_event(event))
> > > +				return -EINVAL;
> > > +
> > > +			/* The metric events cannot be a group leader. */
> > > +			if (leader == event)
> > > +				return -EINVAL;
> > > +
> > > +			/*
> > > +			 * The slots event cannot be the leader of a topdown
> > > +			 * sample-read group, e.g., {slots, topdown-retiring}:S
> > > +			 */
> > > +			if (is_slots_event(leader) && is_sampling_event(leader))
> > > +				return -EINVAL;
> >
> > This has nothing to do with sample-read; SLOTS cannot be sampling when
> > coupled with the METRIC stuff because hardware is daft.
> >
> > And you can have SAMPLE_READ on non-leader events just fine.
> >
> > > +
> > > +			/*
> > > +			 * The slots event must be before the metric events,
> > > +			 * because we only update the values of a topdown
> > > +			 * group once with the slots event.
> > > +			 */
> > > +			if (!is_slots_event(leader)) {
> > > +				for_each_sibling_event(sibling, leader) {
> > > +					if (is_slots_event(sibling))
> > > +						break;
> > > +					if (is_metric_event(sibling))
> > > +						return -EINVAL;
> > > +				}
> > > +			}
> >
> > Per the SIBLING patch this then wants to be:
> >
> > 			if (!is_slots_event(leader))
> > 				return -EINVAL;
> >
> > 			event->event_caps |= PERF_EV_CAP_SIBLING.
> > 			/*
> > 			 * Only once we have a METRICs sibling to we
> > 			 * need TopDown magic.
> > 			 */
> > 			leader->hw.flags |= PERF_X86_EVENT_TOPDOWN;
> > > +		}
> > > +
> > > +		if (!is_sampling_event(event)) {
> > > +			if (event->attr.config1 != 0)
> > > +				return -EINVAL;
> >
> > How does this depend on sampling?
> >
> > > +			/*
> > > +			 * The TopDown metrics events and slots event don't
> > > +			 * support any filters.
> > > +			 */
> > > +			if (event->attr.config & X86_ALL_EVENT_FLAGS)
> > > +				return -EINVAL;
> >
> > That seems independent of sampling too. Even a sampling SLOTS shouldn't
> > be having any of those afaict.
> >
> > > +
> > > +			event->hw.flags |= PERF_X86_EVENT_TOPDOWN;
> >
> > This is confusing too, a !sampling SLOTS event without METRIC siblings
> > shouldn't have this set, right? So arguably, this should be like above.
> >
> > > +
> > > +			event->event_caps |= PERF_EV_CAP_COEXIST;
> > > +
> > > +			if (is_metric_event(event))
> > > +				event->hw.flags &= ~PERF_X86_EVENT_RDPMC_ALLOWED;
> >
> > This too seems like something that should be in the is_metric_event()
> > branch above.
> >
> > > +		}
> > > +	}
> > > +
> > >   	if (!(event->attr.config & ARCH_PERFMON_EVENTSEL_ANY))
> > >   		return 0;
> > >   
>
> FWIW, I pushed out a branch with all these changes in:
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/metric
>
> Just to get it some build love, if you want it differently, I'm happy to
> throw it all out again.

Thanks Peter.

I will pull the branch and do more tests.

Thanks,
Kan