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 e2f6a99f14ab..cc29086e30cd 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 f7a0993c1e7c..ff751a9f182b 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;