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

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

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;

kernel/perf_event.c

@@ -782,6 +782,10 @@ retry:
 	raw_spin_unlock_irq(&ctx->lock);
 }
 
+#define MAX_INTERRUPTS (~0ULL)
+
+static void perf_log_throttle(struct perf_event *event, int enable);
+
 static int
 event_sched_in(struct perf_event *event,
 		 struct perf_cpu_context *cpuctx,
@@ -794,6 +798,17 @@ event_sched_in(struct perf_event *event,
 
 	event->state = PERF_EVENT_STATE_ACTIVE;
 	event->oncpu = smp_processor_id();
+
+	/*
+	 * Unthrottle events, since we scheduled we might have missed several
+	 * ticks already, also for a heavily scheduling task there is little
+	 * guarantee it'll get a tick in a timely manner.
+	 */
+	if (unlikely(event->hw.interrupts == MAX_INTERRUPTS)) {
+		perf_log_throttle(event, 1);
+		event->hw.interrupts = 0;
+	}
+
 	/*
 	 * The new state must be visible before we turn it on in the hardware:
 	 */
@@ -1596,10 +1611,6 @@ void __perf_event_task_sched_in(struct task_struct *task)
 	}
 }
 
-#define MAX_INTERRUPTS (~0ULL)
-
-static void perf_log_throttle(struct perf_event *event, int enable);
-
 static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)
 {
 	u64 frequency = event->attr.sample_freq;