1 files changed, 34 insertions, 11 deletions

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 5bb91bf3d47f..b2abfa18f137 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -180,7 +180,7 @@ armpmu_event_set_period(struct perf_event *event,
 u64
 armpmu_event_update(struct perf_event *event,
 		    struct hw_perf_event *hwc,
-		    int idx, int overflow)
+		    int idx)
 {
 	struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
 	u64 delta, prev_raw_count, new_raw_count;
@@ -193,13 +193,7 @@ again:
 			     new_raw_count) != prev_raw_count)
 		goto again;
 
-	new_raw_count &= armpmu->max_period;
-	prev_raw_count &= armpmu->max_period;
-
-	if (overflow)
-		delta = armpmu->max_period - prev_raw_count + new_raw_count + 1;
-	else
-		delta = new_raw_count - prev_raw_count;
+	delta = (new_raw_count - prev_raw_count) & armpmu->max_period;
 
 	local64_add(delta, &event->count);
 	local64_sub(delta, &hwc->period_left);
@@ -216,7 +210,7 @@ armpmu_read(struct perf_event *event)
 	if (hwc->idx < 0)
 		return;
 
-	armpmu_event_update(event, hwc, hwc->idx, 0);
+	armpmu_event_update(event, hwc, hwc->idx);
 }
 
 static void
@@ -232,7 +226,7 @@ armpmu_stop(struct perf_event *event, int flags)
 	if (!(hwc->state & PERF_HES_STOPPED)) {
 		armpmu->disable(hwc, hwc->idx);
 		barrier(); /* why? */
-		armpmu_event_update(event, hwc, hwc->idx, 0);
+		armpmu_event_update(event, hwc, hwc->idx);
 		hwc->state |= PERF_HES_STOPPED | PERF_HES_UPTODATE;
 	}
 }
@@ -518,7 +512,13 @@ __hw_perf_event_init(struct perf_event *event)
 	hwc->config_base	    |= (unsigned long)mapping;
 
 	if (!hwc->sample_period) {
-		hwc->sample_period  = armpmu->max_period;
+		/*
+		 * For non-sampling runs, limit the sample_period to half
+		 * of the counter width. That way, the new counter value
+		 * is far less likely to overtake the previous one unless
+		 * you have some serious IRQ latency issues.
+		 */
+		hwc->sample_period  = armpmu->max_period >> 1;
 		hwc->last_period    = hwc->sample_period;
 		local64_set(&hwc->period_left, hwc->sample_period);
 	}
@@ -680,6 +680,28 @@ static void __init cpu_pmu_init(struct arm_pmu *armpmu)
 }
 
 /*
+ * PMU hardware loses all context when a CPU goes offline.
+ * When a CPU is hotplugged back in, since some hardware registers are
+ * UNKNOWN at reset, the PMU must be explicitly reset to avoid reading
+ * junk values out of them.
+ */
+static int __cpuinit pmu_cpu_notify(struct notifier_block *b,
+					unsigned long action, void *hcpu)
+{
+	if ((action & ~CPU_TASKS_FROZEN) != CPU_STARTING)
+		return NOTIFY_DONE;
+
+	if (cpu_pmu && cpu_pmu->reset)
+		cpu_pmu->reset(NULL);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata pmu_cpu_notifier = {
+	.notifier_call = pmu_cpu_notify,
+};
+
+/*
  * CPU PMU identification and registration.
  */
 static int __init
@@ -730,6 +752,7 @@ init_hw_perf_events(void)
 		pr_info("enabled with %s PMU driver, %d counters available\n",
 			cpu_pmu->name, cpu_pmu->num_events);
 		cpu_pmu_init(cpu_pmu);
+		register_cpu_notifier(&pmu_cpu_notifier);
 		armpmu_register(cpu_pmu, "cpu", PERF_TYPE_RAW);
 	} else {
 		pr_info("no hardware support available\n");