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>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 84451c0debba..257eccf9afd4 100644
--- 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;