perf: Simplify the branch stack check

Use event->attr.branch_sample_type to replace
intel_pmu_needs_lbr_smpl() for avoiding duplicated code that
implicitly enables the LBR.

Currently, branch stack can be enabled by user explicitly requesting
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@intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: eranian@google.com
Cc: jolsa@redhat.com
Link: http://lkml.kernel.org/r/1415156173-10035-11-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index a485ba1244762d39c76d1217450533a5933f417c..9f1dd18fa3957540f73e1f93653186dbbf5152f3 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1029,20 +1029,6 @@ 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 = this_cpu_ptr(&cpu_hw_events);
@@ -1207,7 +1193,7 @@ 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)) {
@@ -1268,7 +1254,7 @@ 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)
@@ -1747,7 +1733,7 @@ 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 270cd0173e61132e2034548819664ad59dcc5a15..43cc158487e602c49145619b5f377eea0f75f57b 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -814,6 +814,11 @@ 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 84451c0debbacc8c85cd4c2045ce7b62a1c384f0..257eccf9afd4c5dd3486e93ad55dd72c17a856e5 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7232,6 +7232,9 @@ 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;