[tip:perf/core] perf/x86/intel/lbr: Optimize v4 LBR unfreezing

[tip-bot for Andi Kleen <tipbot@zytor.com>]

Commit-ID:  425507fa5f321bb5ce1b5eb57a9586e0cf0b9802
Gitweb:     http://git.kernel.org/tip/425507fa5f321bb5ce1b5eb57a9586e0cf0b9802
Author:     Andi Kleen <ak@linux.intel.com>
AuthorDate: Sun, 10 May 2015 12:22:46 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 4 Aug 2015 10:16:58 +0200

perf/x86/intel/lbr: Optimize v4 LBR unfreezing

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@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/1431285767-27027-9-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 2fb5737..769a42f 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -141,6 +141,13 @@ 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.
 	 */