[PATCH] perf, x86: catch spurious interrupts after disabling counters

[Robert Richter <robert.richter@amd.com>]

On 14.09.10 19:41:32, Robert Richter wrote:
> I found the reason why we get the unknown nmi. For some reason
> cpuc->active_mask in x86_pmu_handle_irq() is zero. Thus, no counters
> are handled when we get an nmi. It seems there is somewhere a race
> accessing the active_mask. So far I don't have a fix available.
> Changing x86_pmu_stop() did not help:

The patch below for tip/perf/urgent fixes this.

-Robert

>From 4206a086f5b37efc1b4d94f1d90b55802b299ca0 Mon Sep 17 00:00:00 2001
From: Robert Richter <robert.richter@amd.com>
Date: Wed, 15 Sep 2010 16:12:59 +0200
Subject: [PATCH] perf, x86: catch spurious interrupts after disabling counters

Some cpus still deliver spurious interrupts after disabling a counter.
This caused 'undelivered NMI' messages. This patch fixes this.

Signed-off-by: Robert Richter <robert.richter@amd.com>
---
 arch/x86/kernel/cpu/perf_event.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 3efdf28..df7aabd 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -102,6 +102,7 @@ struct cpu_hw_events {
 	 */
 	struct perf_event	*events[X86_PMC_IDX_MAX]; /* in counter order */
 	unsigned long		active_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
+	unsigned long		running[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
 	int			enabled;
 
 	int			n_events;
@@ -1010,6 +1011,7 @@ static int x86_pmu_start(struct perf_event *event)
 	x86_perf_event_set_period(event);
 	cpuc->events[idx] = event;
 	__set_bit(idx, cpuc->active_mask);
+	__set_bit(idx, cpuc->running);
 	x86_pmu.enable(event);
 	perf_event_update_userpage(event);
 
@@ -1141,8 +1143,17 @@ static int x86_pmu_handle_irq(struct pt_regs *regs)
 	cpuc = &__get_cpu_var(cpu_hw_events);
 
 	for (idx = 0; idx < x86_pmu.num_counters; idx++) {
-		if (!test_bit(idx, cpuc->active_mask))
+		if (!test_bit(idx, cpuc->active_mask)) {
+			if (__test_and_clear_bit(idx, cpuc->running))
+				/*
+				 * Though we deactivated the counter
+				 * some cpus might still deliver
+				 * spurious interrupts. Catching them
+				 * here.
+				 */
+				handled++;
 			continue;
+		}
 
 		event = cpuc->events[idx];
 		hwc = &event->hw;
-- 
1.7.2.2





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