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

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Date:	Thu, 5 Aug 2010 19:09:17 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH] perf,x86: P4 PMU -- update nmi irq statistics and unmask
	lvt entry properly

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@...el.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
CC: Lin Ming <ming.m.lin@...el.com>
CC: Stephane Eranian <eranian@...gle.com>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Ingo Molnar <mingo@...e.hu>
CC: Frederic Weisbecker <fweisbec@...il.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;
 }
 
 /*
--
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