cpuidle: add a repeating pattern detector to the menu governor

[karo-tx-linux.git] / drivers / cpuidle / governors / menu.c

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 1aea7157d8fffa603ca79d4cca7552db0bb313bd..52ff8aa63f8449b04d5bcd046b028e23dcf6d68b 100644 (file)
--- 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
@@ -100,11 +113,12 @@ struct menu_device {
        int             needs_update;
 
        unsigned int    expected_us;
-       unsigned int    measured_us;
        u64             predicted_us;
        unsigned int    exit_us;
        unsigned int    bucket;
        u64             correction_factor[BUCKETS];
+       u32             intervals[INTERVALS];
+       int             interval_ptr;
 };
 
 
@@ -176,6 +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
@@ -183,18 +233,18 @@ static u64 div_round64(u64 dividend, u32 divisor)
 static int menu_select(struct cpuidle_device *dev)
 {
        struct menu_device *data = &__get_cpu_var(menu_devices);
-       int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
+       int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
        int i;
        int multiplier;
 
-       data->last_state_idx = 0;
-       data->exit_us = 0;
-
        if (data->needs_update) {
                menu_update(dev);
                data->needs_update = 0;
        }
 
+       data->last_state_idx = 0;
+       data->exit_us = 0;
+
        /* Special case when user has set very strict latency requirement */
        if (unlikely(latency_req == 0))
                return 0;
@@ -219,6 +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.
@@ -294,7 +346,7 @@ static void menu_update(struct cpuidle_device *dev)
        new_factor = data->correction_factor[data->bucket]
                        * (DECAY - 1) / DECAY;
 
-       if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
+       if (data->expected_us > 0 && measured_us < MAX_INTERESTING)
                new_factor += RESOLUTION * measured_us / data->expected_us;
        else
                /*
@@ -311,6 +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;
 }
 
 /**