perf, x86: Clear the LBRs on init

Some CPUs have errata where the LBR is not cleared on Power-On. So always
clear the LBRs before use.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
LKML-Reference: <20100305154128.966563424@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 19 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 224c952071f9..c135ed735b22 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -767,6 +767,20 @@ static __initconst struct x86_pmu core_pmu = {
         .event_constraints      = intel_core_event_constraints,
 };
 
+static void intel_pmu_cpu_starting(int cpu)
+{
+        init_debug_store_on_cpu(cpu);
+        /*
+         * Deal with CPUs that don't clear their LBRs on power-up.
+         */
+        intel_pmu_lbr_reset();
+}
+
+static void intel_pmu_cpu_dying(int cpu)
+{
+        fini_debug_store_on_cpu(cpu);
+}
+
 static __initconst struct x86_pmu intel_pmu = {
         .name                   = "Intel",
         .handle_irq             = intel_pmu_handle_irq,
@@ -788,8 +802,8 @@ static __initconst struct x86_pmu intel_pmu = {
         .max_period             = (1ULL << 31) - 1,
         .get_event_constraints  = intel_get_event_constraints,
 
-        .cpu_starting           = init_debug_store_on_cpu,
-        .cpu_dying              = fini_debug_store_on_cpu,
+        .cpu_starting           = intel_pmu_cpu_starting,
+        .cpu_dying              = intel_pmu_cpu_dying,
 };
 
 static void intel_clovertown_quirks(void)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 4f3a124329c4..dcec765f8188 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -53,6 +53,9 @@ static void intel_pmu_lbr_reset_64(void)
 
 static void intel_pmu_lbr_reset(void)
 {
+        if (!x86_pmu.lbr_nr)
+                return;
+
         if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_32)
                 intel_pmu_lbr_reset_32();
         else