1 files changed, 34 insertions, 11 deletions

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 5bb91bf3d47..b2abfa18f13 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");