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

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

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