[PATCH V3 2/6] perf/x86: Add PERF_X86_EVENT_NEEDS_BRANCH_STACK flag

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

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 with the new PERF_SAMPLE_BRANCH_EVT_CNTRS 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_EVT_CNTRS into account.

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---

New patch

 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 0f4ce79de4f8..8434315b765f 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2518,9 +2518,14 @@ 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);
@@ -2831,7 +2836,7 @@ 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);
 }
 
@@ -3908,7 +3913,10 @@ 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