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    SubjectRe: [PATCH V4 4/7] perf/x86/intel: Support LBR event logging
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    On 2023-10-19 7:09 a.m., Peter Zijlstra wrote:
    > On Wed, Oct 04, 2023 at 11:40:41AM -0700, kan.liang@linux.intel.com wrote:
    >
    >> @@ -3905,6 +3915,44 @@ static int intel_pmu_hw_config(struct perf_event *event)
    >> if (needs_branch_stack(event) && is_sampling_event(event))
    >> event->hw.flags |= PERF_X86_EVENT_NEEDS_BRANCH_STACK;
    >>
    >> + if (branch_sample_counters(event)) {
    >> + struct perf_event *leader, *sibling;
    >> +
    >> + if (!(x86_pmu.flags & PMU_FL_LBR_EVENT) ||
    >> + (event->attr.config & ~INTEL_ARCH_EVENT_MASK))
    >> + return -EINVAL;
    >> +
    >> + /*
    >> + * The event logging is not supported in the call stack mode
    >> + * yet, since we cannot simply flush the LBR during e.g.,
    >> + * multiplexing. Also, there is no obvious usage with the call
    >> + * stack mode. Simply forbids it for now.
    >> + *
    >> + * If any events in the group enable the LBR event logging
    >> + * feature, the group is treated as a LBR event logging group,
    >> + * which requires the extra space to store the counters.
    >> + */
    >> + leader = event->group_leader;
    >> + if (branch_sample_call_stack(leader))
    >> + return -EINVAL;
    >> + leader->hw.flags |= PERF_X86_EVENT_BRANCH_COUNTERS;
    >
    > (superfluous whitespace before operator)
    >
    >> +
    >> + for_each_sibling_event(sibling, leader) {
    >> + if (branch_sample_call_stack(sibling))
    >> + return -EINVAL;
    >> + }
    >> +
    >> + /*
    >> + * Only applying the PERF_SAMPLE_BRANCH_COUNTERS doesn't
    >> + * require any branch stack setup.
    >> + * Clear the bit to avoid unnecessary branch stack setup.
    >> + */
    >> + if (0 == (event->attr.branch_sample_type &
    >> + ~(PERF_SAMPLE_BRANCH_PLM_ALL |
    >> + PERF_SAMPLE_BRANCH_COUNTERS)))
    >> + event->hw.flags &= ~PERF_X86_EVENT_NEEDS_BRANCH_STACK;
    >> + }
    >
    > Does this / should this check the number of group members vs supported
    > number of lbr counters?

    Sure, I will add the check here for the numbers, so perf can error out
    earlier.

    Thanks,
    Kan

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