[PATCH V6 10/17] perf, core: simplify need branch stack check

[Kan Liang]

Using event->attr.branch_sample_type to replace
intel_pmu_needs_lbr_smpl() for avoiding duplicating code
that implicitly enables the LBR.
Currently, branch stack can be enabled by user explicitly requested
branch sampling or implicit branch sampling to correct PEBS skid.
For user explicitly requested branch sampling, the branch_sample_type is
explicitly set by user. For PEBS case, the branch_sample_type is also
implicitly set to PERF_SAMPLE_BRANCH_ANY in x86_pmu_hw_config.

Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
---
 arch/x86/kernel/cpu/perf_event_intel.c | 20 +++-----------------
 include/linux/perf_event.h             |  5 +++++
 kernel/events/core.c                   |  3 +++
 3 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index e8c690e..50bb51d 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1158,20 +1158,6 @@ static __initconst const u64 slm_hw_cache_event_ids
  },
 };
 
-static inline bool intel_pmu_needs_lbr_smpl(struct perf_event *event)
-{
-	/* user explicitly requested branch sampling */
-	if (has_branch_stack(event))
-		return true;
-
-	/* implicit branch sampling to correct PEBS skid */
-	if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1 &&
-	    x86_pmu.intel_cap.pebs_format < 2)
-		return true;
-
-	return false;
-}
-
 static void intel_pmu_disable_all(void)
 {
 	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
@@ -1336,7 +1322,7 @@ static void intel_pmu_disable_event(struct perf_event *event)
 	 * must disable before any actual event
 	 * because any event may be combined with LBR
 	 */
-	if (intel_pmu_needs_lbr_smpl(event))
+	if (needs_branch_stack(event))
 		intel_pmu_lbr_disable(event);
 
 	if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) {
@@ -1397,7 +1383,7 @@ static void intel_pmu_enable_event(struct perf_event *event)
 	 * must enabled before any actual event
 	 * because any event may be combined with LBR
 	 */
-	if (intel_pmu_needs_lbr_smpl(event))
+	if (needs_branch_stack(event))
 		intel_pmu_lbr_enable(event);
 
 	if (event->attr.exclude_host)
@@ -1876,7 +1862,7 @@ static int intel_pmu_hw_config(struct perf_event *event)
 	if (event->attr.precise_ip && x86_pmu.pebs_aliases)
 		x86_pmu.pebs_aliases(event);
 
-	if (intel_pmu_needs_lbr_smpl(event)) {
+	if (needs_branch_stack(event)) {
 		ret = intel_pmu_setup_lbr_filter(event);
 		if (ret)
 			return ret;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 159e092..285776a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -791,6 +791,11 @@ static inline bool has_branch_stack(struct perf_event *event)
 	return event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK;
 }
 
+static inline bool needs_branch_stack(struct perf_event *event)
+{
+	return event->attr.branch_sample_type != 0;
+}
+
 extern int perf_output_begin(struct perf_output_handle *handle,
 			     struct perf_event *event, unsigned int size);
 extern void perf_output_end(struct perf_output_handle *handle);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5b5f143..c8e367c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7028,6 +7028,9 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 	if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))
 		goto err_ns;
 
+	if (!has_branch_stack(event))
+		event->attr.branch_sample_type = 0;
+
 	pmu = perf_init_event(event);
 	if (!pmu)
 		goto err_ns;
-- 
1.8.3.2

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