[tip:perf/core] perf/x86/intel: Move PMU ACK to after LBR read

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

Commit-ID:  0f29e573dd32bb8598e74271454e97c962da5e05
Gitweb:     http://git.kernel.org/tip/0f29e573dd32bb8598e74271454e97c962da5e05
Author:     Andi Kleen <ak@linux.intel.com>
AuthorDate: Sun, 10 May 2015 12:22:47 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 4 Aug 2015 10:16:58 +0200

perf/x86/intel: Move PMU ACK to after LBR read

With Arch Perfmon v4 the PMU ack unfreezes the LBRs. So we need to do
the PMU ack after the LBR reading, otherwise the LBRs would be polluted
by the PMI handler.

This is a minimal change. In principle the ACK could be moved much later.

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/1431285767-27027-10-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/cpu/perf_event_intel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 52c9ded..da93b4b 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1594,6 +1594,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 
 	loops = 0;
 again:
+	intel_pmu_lbr_read();
 	intel_pmu_ack_status(status);
 	if (++loops > 100) {
 		static bool warned = false;
@@ -1608,7 +1609,6 @@ again:
 
 	inc_irq_stat(apic_perf_irqs);
 
-	intel_pmu_lbr_read();
 
 	/*
 	 * Ignore a range of extra bits in status that do not indicate