[PATCH] perf,x86: P4 PMU -- update nmi irq statistics and unmask lvt entry properly

[Cyrill Gorcunov <gorcunov@openvz.org>]

In case if last active performance counter is not overflowed at
moment of NMI being triggered by another counter, the irq statistics
may miss an update stage. As a more serious consequence -- apic quirk
may not be triggered so apic lvt entry stay masked.

Tested-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Lin Ming <ming.m.lin@intel.com>
CC: Stephane Eranian <eranian@google.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Ingo Molnar <mingo@elte.hu>
CC: Frederic Weisbecker <fweisbec@gmail.com>
---
 arch/x86/kernel/cpu/perf_event_p4.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
@@ -656,6 +656,7 @@ static int p4_pmu_handle_irq(struct pt_r
 	cpuc = &__get_cpu_var(cpu_hw_events);
 
 	for (idx = 0; idx < x86_pmu.num_counters; idx++) {
+		int overflow;
 
 		if (!test_bit(idx, cpuc->active_mask))
 			continue;
@@ -666,12 +667,14 @@ static int p4_pmu_handle_irq(struct pt_r
 		WARN_ON_ONCE(hwc->idx != idx);
 
 		/* it might be unflagged overflow */
-		handled = p4_pmu_clear_cccr_ovf(hwc);
+		overflow = p4_pmu_clear_cccr_ovf(hwc);
 
 		val = x86_perf_event_update(event);
-		if (!handled && (val & (1ULL << (x86_pmu.cntval_bits - 1))))
+		if (!overflow && (val & (1ULL << (x86_pmu.cntval_bits - 1))))
 			continue;
 
+		handled += overflow;
+
 		/* event overflow for sure */
 		data.period = event->hw.last_period;
 
@@ -687,7 +690,7 @@ static int p4_pmu_handle_irq(struct pt_r
 		inc_irq_stat(apic_perf_irqs);
 	}
 
-	return handled;
+	return handled > 0;
 }
 
 /*