perf/x86/intel/lbr: Optimize v4 LBR unfreezing

In Arch perfmon v4 the GLOBAL_STATUS reset automatically unfreezes
LBRs. So no need to do it manually in the LBR code. Add a check
to skip it.

v2: Move test up to beginning of function.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/1431285767-27027-9-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 2fb57373beca72f5121458f0ec2cb9cdae751634..769a42f874dce3f0425164a2abb0a2d03d7ac9ba 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -140,6 +140,13 @@ static void __intel_pmu_lbr_enable(bool pmi)
        struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
        u64 debugctl, lbr_select = 0, orig_debugctl;
 
+       /*
+        * No need to unfreeze manually, as v4 can do that as part
+        * of the GLOBAL_STATUS ack.
+        */
+       if (pmi && x86_pmu.version >= 4)
+               return;
+
        /*
         * No need to reprogram LBR_SELECT in a PMI, as it
         * did not change.