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    Subject[PATCH V5 2/8] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH_STACK flag
    Date
    From: Kan Liang <kan.liang@linux.intel.com>

    Currently, branch_sample_type !=0 is used to check whether a branch
    stack setup is required. But it doesn't check the sample type,
    unnecessary branch stack setup may be done for a counting event. E.g.,
    perf record -e "{branch-instructions,branch-misses}:S" -j any
    Also, the event only with the new PERF_SAMPLE_BRANCH_COUNTERS branch
    sample type may not require a branch stack setup either.

    Add a new flag NEEDS_BRANCH_STACK to indicate whether the event requires
    a branch stack setup. Replace the needs_branch_stack() by checking the
    new flag.

    The counting event check is implemented here. The later patch will take
    the new PERF_SAMPLE_BRANCH_COUNTERS into account.

    Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
    ---

    No changes since V4

    arch/x86/events/intel/core.c | 14 +++++++++++---
    arch/x86/events/perf_event_flags.h | 1 +
    2 files changed, 12 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
    index 41a164764a84..a99449c0d77c 100644
    --- a/arch/x86/events/intel/core.c
    +++ b/arch/x86/events/intel/core.c
    @@ -2527,9 +2527,14 @@ static void intel_pmu_assign_event(struct perf_event *event, int idx)
    perf_report_aux_output_id(event, idx);
    }

    +static __always_inline bool intel_pmu_needs_branch_stack(struct perf_event *event)
    +{
    + return event->hw.flags & PERF_X86_EVENT_NEEDS_BRANCH_STACK;
    +}
    +
    static void intel_pmu_del_event(struct perf_event *event)
    {
    - if (needs_branch_stack(event))
    + if (intel_pmu_needs_branch_stack(event))
    intel_pmu_lbr_del(event);
    if (event->attr.precise_ip)
    intel_pmu_pebs_del(event);
    @@ -2820,7 +2825,7 @@ static void intel_pmu_add_event(struct perf_event *event)
    {
    if (event->attr.precise_ip)
    intel_pmu_pebs_add(event);
    - if (needs_branch_stack(event))
    + if (intel_pmu_needs_branch_stack(event))
    intel_pmu_lbr_add(event);
    }

    @@ -3897,7 +3902,10 @@ static int intel_pmu_hw_config(struct perf_event *event)
    x86_pmu.pebs_aliases(event);
    }

    - if (needs_branch_stack(event)) {
    + if (needs_branch_stack(event) && is_sampling_event(event))
    + event->hw.flags |= PERF_X86_EVENT_NEEDS_BRANCH_STACK;
    +
    + if (intel_pmu_needs_branch_stack(event)) {
    ret = intel_pmu_setup_lbr_filter(event);
    if (ret)
    return ret;
    diff --git a/arch/x86/events/perf_event_flags.h b/arch/x86/events/perf_event_flags.h
    index 1dc19b9b4426..a1685981c520 100644
    --- a/arch/x86/events/perf_event_flags.h
    +++ b/arch/x86/events/perf_event_flags.h
    @@ -20,3 +20,4 @@ PERF_ARCH(TOPDOWN, 0x04000) /* Count Topdown slots/metrics events */
    PERF_ARCH(PEBS_STLAT, 0x08000) /* st+stlat data address sampling */
    PERF_ARCH(AMD_BRS, 0x10000) /* AMD Branch Sampling */
    PERF_ARCH(PEBS_LAT_HYBRID, 0x20000) /* ld and st lat for hybrid */
    +PERF_ARCH(NEEDS_BRANCH_STACK, 0x40000) /* require branch stack setup */
    --
    2.35.1
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