Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  perf: Fix throttle logic
  perf, x86: P4 PMU: Fix spurious NMI messages

2 files changed, 9 insertions, 3 deletions

diff --git a/arch/x86/include/asm/perf_event_p4.h b/arch/x86/include/asm/perf_event_p4.h
index e2f6a99..cc29086 100644
--- a/arch/x86/include/asm/perf_event_p4.h
+++ b/arch/x86/include/asm/perf_event_p4.h
@@ -22,6 +22,7 @@
 
 #define ARCH_P4_CNTRVAL_BITS	(40)
 #define ARCH_P4_CNTRVAL_MASK	((1ULL << ARCH_P4_CNTRVAL_BITS) - 1)
+#define ARCH_P4_UNFLAGGED_BIT	((1ULL) << (ARCH_P4_CNTRVAL_BITS - 1))
 
 #define P4_ESCR_EVENT_MASK	0x7e000000U
 #define P4_ESCR_EVENT_SHIFT	25
diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index f7a0993..ff751a9 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -770,9 +770,14 @@ static inline int p4_pmu_clear_cccr_ovf(struct hw_perf_event *hwc)
 		return 1;
 	}
 
-	/* it might be unflagged overflow */
-	rdmsrl(hwc->event_base + hwc->idx, v);
-	if (!(v & ARCH_P4_CNTRVAL_MASK))
+	/*
+	 * In some circumstances the overflow might issue an NMI but did
+	 * not set P4_CCCR_OVF bit. Because a counter holds a negative value
+	 * we simply check for high bit being set, if it's cleared it means
+	 * the counter has reached zero value and continued counting before
+	 * real NMI signal was received:
+	 */
+	if (!(v & ARCH_P4_UNFLAGGED_BIT))
 		return 1;
 
 	return 0;