perf, x86: Fix BTS condition

Currently the x86 backend incorrectly assumes that any BRANCH_INSN
with sample_period==1 is a BTS request. This is not true when we do
frequency driven profiling such as 'perf record -e branches'.

Solves this error:

  $ perf record -e branches ./array
  Error: sys_perf_event_open() syscall returned with 95 (Operation not supported).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: "Metzger, Markus T" <markus.t.metzger@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/n/tip-rd2y4ct71hjawzz6fpvsy9hg@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 5 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 632e5dc9c9c0..fac0654021b8 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -613,8 +613,8 @@ static int x86_setup_perfctr(struct perf_event *event)
         /*
          * Branch tracing:
          */
-        if ((attr->config == PERF_COUNT_HW_BRANCH_INSTRUCTIONS) &&
-            (hwc->sample_period == 1)) {
+        if (attr->config == PERF_COUNT_HW_BRANCH_INSTRUCTIONS &&
+            !attr->freq && hwc->sample_period == 1) {
                 /* BTS is not supported by this architecture. */
                 if (!x86_pmu.bts_active)
                         return -EOPNOTSUPP;
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 43fa20b13817..9194b0698d63 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -998,6 +998,9 @@ intel_bts_constraints(struct perf_event *event)
         struct hw_perf_event *hwc = &event->hw;
         unsigned int hw_event, bts_event;
 
+        if (event->attr.freq)
+                return NULL;
+
         hw_event = hwc->config & INTEL_ARCH_EVENT_MASK;
         bts_event = x86_pmu.event_map(PERF_COUNT_HW_BRANCH_INSTRUCTIONS);