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    SubjectRe: [PATCH V7 08/14] perf/x86/intel: Generic support for hardware TopDown metrics
    On Thu, Jul 23, 2020 at 10:11:11AM -0700, kan.liang@linux.intel.com 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;
    >

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