perf/x86: Disable LBR support for older Intel Atom processors

The patch adds a restriction for Intel Atom LBR support. Only
steppings 10 (PineView) and more recent are supported. Older models
do not have a functional LBR. Their LBR does not freeze on PMU
interrupt which makes LBR unusable in the context of perf_events.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1328826068-11713-7-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index e54a063..07f0ff8 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -315,6 +315,16 @@ void intel_pmu_lbr_init_snb(void)
 /* atom */
 void intel_pmu_lbr_init_atom(void)
 {
+       /*
+        * only models starting at stepping 10 seems
+        * to have an operational LBR which can freeze
+        * on PMU interrupt
+        */
+       if (boot_cpu_data.x86_mask < 10) {
+               pr_cont("LBR disabled due to erratum");
+               return;
+       }
+
        x86_pmu.lbr_nr     = 8;
        x86_pmu.lbr_tos    = MSR_LBR_TOS;
        x86_pmu.lbr_from   = MSR_LBR_CORE_FROM;