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Diffstat (limited to 'drivers/cpuidle/governors/menu.c')
-rw-r--r--drivers/cpuidle/governors/menu.c60
1 files changed, 59 insertions, 1 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index b81ad9c..52ff8aa 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;
}
/**
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