5 files changed, 16 insertions, 16 deletions

diff --git a/arch/arm/include/asm/pmu.h b/arch/arm/include/asm/pmu.h
index b5a5be2536c1..90114faa9f3c 100644
--- a/arch/arm/include/asm/pmu.h
+++ b/arch/arm/include/asm/pmu.h
@@ -134,7 +134,7 @@ int __init armpmu_register(struct arm_pmu *armpmu, char *name, int type);
 
 u64 armpmu_event_update(struct perf_event *event,
                         struct hw_perf_event *hwc,
-                        int idx, int overflow);
+                        int idx);
 
 int armpmu_event_set_period(struct perf_event *event,
                             struct hw_perf_event *hwc,
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 5bb91bf3d47f..56173ae16448 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);
         }
diff --git a/arch/arm/kernel/perf_event_v6.c b/arch/arm/kernel/perf_event_v6.c
index 533be9930ec2..88bf15253fbd 100644
--- a/arch/arm/kernel/perf_event_v6.c
+++ b/arch/arm/kernel/perf_event_v6.c
@@ -524,7 +524,7 @@ armv6pmu_handle_irq(int irq_num,
                         continue;
 
                 hwc = &event->hw;
-                armpmu_event_update(event, hwc, idx, 1);
+                armpmu_event_update(event, hwc, idx);
                 data.period = event->hw.last_period;
                 if (!armpmu_event_set_period(event, hwc, idx))
                         continue;
diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index 6933244c68f9..6f488610f8fc 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -963,7 +963,7 @@ static irqreturn_t armv7pmu_handle_irq(int irq_num, void *dev)
                         continue;
 
                 hwc = &event->hw;
-                armpmu_event_update(event, hwc, idx, 1);
+                armpmu_event_update(event, hwc, idx);
                 data.period = event->hw.last_period;
                 if (!armpmu_event_set_period(event, hwc, idx))
                         continue;
diff --git a/arch/arm/kernel/perf_event_xscale.c b/arch/arm/kernel/perf_event_xscale.c
index 3b99d8269829..831e019b017c 100644
--- a/arch/arm/kernel/perf_event_xscale.c
+++ b/arch/arm/kernel/perf_event_xscale.c
@@ -259,7 +259,7 @@ xscale1pmu_handle_irq(int irq_num, void *dev)
                         continue;
 
                 hwc = &event->hw;
-                armpmu_event_update(event, hwc, idx, 1);
+                armpmu_event_update(event, hwc, idx);
                 data.period = event->hw.last_period;
                 if (!armpmu_event_set_period(event, hwc, idx))
                         continue;
@@ -596,7 +596,7 @@ xscale2pmu_handle_irq(int irq_num, void *dev)
                         continue;
 
                 hwc = &event->hw;
-                armpmu_event_update(event, hwc, idx, 1);
+                armpmu_event_update(event, hwc, idx);
                 data.period = event->hw.last_period;
                 if (!armpmu_event_set_period(event, hwc, idx))
                         continue;