[PATCH 8/9] perf, x86: Optimize v4 LBR unfreezing

Andi Kleen
2015-05-07T22:57:38Z

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.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 6c48c97..64d3122 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -147,6 +147,13 @@ static void __intel_pmu_lbr_enable(bool pmi)
wrmsrl(MSR_LBR_SELECT, lbr_select);
}

+ /*
+ * No need to unfreeze manually, as v4 can do that as part
+ * of the GLOBAL_STATUS ack.
+ */
+ if (pmi && x86_pmu.version >= 4)
+ return;
+
rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
orig_debugctl = debugctl;
debugctl |= DEBUGCTLMSR_LBR;
--
1.9.3