1 files changed, 59 insertions, 1 deletions

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index b81ad9c731ae..52ff8aa63f84 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -21,9 +21,12 @@
 #include <linux/math64.h>
 
 #define BUCKETS 12
+#define INTERVALS 8
 #define RESOLUTION 1024
-#define DECAY 4
+#define DECAY 8
 #define MAX_INTERESTING 50000
+#define STDDEV_THRESH 400
+
 
 /*
  * Concepts and ideas behind the menu governor
@@ -64,6 +67,16 @@
  * indexed based on the magnitude of the expected duration as well as the
  * "is IO outstanding" property.
  *
+ * Repeatable-interval-detector
+ * ----------------------------
+ * There are some cases where "next timer" is a completely unusable predictor:
+ * Those cases where the interval is fixed, for example due to hardware
+ * interrupt mitigation, but also due to fixed transfer rate devices such as
+ * mice.
+ * For this, we use a different predictor: We track the duration of the last 8
+ * intervals and if the stand deviation of these 8 intervals is below a
+ * threshold value, we use the average of these intervals as prediction.
+ *
  * Limiting Performance Impact
  * ---------------------------
  * C states, especially those with large exit latencies, can have a real
@@ -104,6 +117,8 @@ struct menu_device {
         unsigned int    exit_us;
         unsigned int    bucket;
         u64             correction_factor[BUCKETS];
+        u32             intervals[INTERVALS];
+        int             interval_ptr;
 };
 
 
@@ -175,6 +190,42 @@ static u64 div_round64(u64 dividend, u32 divisor)
         return div_u64(dividend + (divisor / 2), divisor);
 }
 
+/*
+ * Try detecting repeating patterns by keeping track of the last 8
+ * intervals, and checking if the standard deviation of that set
+ * of points is below a threshold. If it is... then use the
+ * average of these 8 points as the estimated value.
+ */
+static void detect_repeating_patterns(struct menu_device *data)
+{
+        int i;
+        uint64_t avg = 0;
+        uint64_t stddev = 0; /* contains the square of the std deviation */
+
+        /* first calculate average and standard deviation of the past */
+        for (i = 0; i < INTERVALS; i++)
+                avg += data->intervals[i];
+        avg = avg / INTERVALS;
+
+        /* if the avg is beyond the known next tick, it's worthless */
+        if (avg > data->expected_us)
+                return;
+
+        for (i = 0; i < INTERVALS; i++)
+                stddev += (data->intervals[i] - avg) *
+                          (data->intervals[i] - avg);
+
+        stddev = stddev / INTERVALS;
+
+        /*
+         * now.. if stddev is small.. then assume we have a
+         * repeating pattern and predict we keep doing this.
+         */
+
+        if (avg && stddev < STDDEV_THRESH)
+                data->predicted_us = avg;
+}
+
 /**
  * menu_select - selects the next idle state to enter
  * @dev: the CPU
@@ -218,6 +269,8 @@ static int menu_select(struct cpuidle_device *dev)
         data->predicted_us = div_round64(data->expected_us * data->correction_factor[data->bucket],
                                          RESOLUTION * DECAY);
 
+        detect_repeating_patterns(data);
+
         /*
          * We want to default to C1 (hlt), not to busy polling
          * unless the timer is happening really really soon.
@@ -310,6 +363,11 @@ static void menu_update(struct cpuidle_device *dev)
                 new_factor = 1;
 
         data->correction_factor[data->bucket] = new_factor;
+
+        /* update the repeating-pattern data */
+        data->intervals[data->interval_ptr++] = last_idle_us;
+        if (data->interval_ptr >= INTERVALS)
+                data->interval_ptr = 0;
 }
 
 /**