1 files changed, 26 insertions, 18 deletions

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index f0995dd2469f..b347c101c1f7 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -387,32 +387,40 @@ static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = &__get_cpu_var(menu_devices);
 	int last_idx = data->last_state_idx;
-	unsigned int last_idle_us = cpuidle_get_last_residency(dev);
 	struct cpuidle_state *target = &drv->states[last_idx];
 	unsigned int measured_us;
 	unsigned int new_factor;
 
 	/*
-	 * Ugh, this idle state doesn't support residency measurements, so we
-	 * are basically lost in the dark.  As a compromise, assume we slept
-	 * for the whole expected time.
+	 * Try to figure out how much time passed between entry to low
+	 * power state and occurrence of the wakeup event.
+	 *
+	 * If the entered idle state didn't support residency measurements,
+	 * we are basically lost in the dark how much time passed.
+	 * As a compromise, assume we slept for the whole expected time.
+	 *
+	 * Any measured amount of time will include the exit latency.
+	 * Since we are interested in when the wakeup begun, not when it
+	 * was completed, we must substract the exit latency. However, if
+	 * the measured amount of time is less than the exit latency,
+	 * assume the state was never reached and the exit latency is 0.
 	 */
-	if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID)))
-		last_idle_us = data->next_timer_us;
-
+	if (unlikely(!(target->flags & CPUIDLE_FLAG_TIME_VALID))) {
+		/* Use timer value as is */
+		measured_us = data->next_timer_us;
 
-	measured_us = last_idle_us;
+	} else {
+		/* Use measured value */
+		measured_us = cpuidle_get_last_residency(dev);
 
-	/*
-	 * We correct for the exit latency; we are assuming here that the
-	 * exit latency happens after the event that we're interested in.
-	 */
-	if (measured_us > target->exit_latency)
-		measured_us -= target->exit_latency;
+		/* Deduct exit latency */
+		if (measured_us > target->exit_latency)
+			measured_us -= target->exit_latency;
 
-	/* Make sure our coefficients do not exceed unity */
-	if (measured_us > data->next_timer_us)
-		measured_us = data->next_timer_us;
+		/* Make sure our coefficients do not exceed unity */
+		if (measured_us > data->next_timer_us)
+			measured_us = data->next_timer_us;
+	}
 
 	/* Update our correction ratio */
 	new_factor = data->correction_factor[data->bucket];
@@ -439,7 +447,7 @@ static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	data->correction_factor[data->bucket] = new_factor;
 
 	/* update the repeating-pattern data */
-	data->intervals[data->interval_ptr++] = last_idle_us;
+	data->intervals[data->interval_ptr++] = measured_us;
 	if (data->interval_ptr >= INTERVALS)
 		data->interval_ptr = 0;
 }