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

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Date:	Sun, 10 May 2015 12:22:46 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	peterz@...radead.org
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 8/9] x86, perf: Optimize v4 LBR unfreezing

From: Andi Kleen <ak@...ux.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.

v2: Move test up to beginning of function.
Signed-off-by: Andi Kleen <ak@...ux.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..ae54ea9 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -139,6 +139,13 @@ static void __intel_pmu_lbr_enable(bool pmi)
 	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.
 	 */
-- 
1.9.3

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