Using bitshifts instead of division and multiplication should improve
performance. That requires weight and factor to be powers of two, but i think
this is something we can live with.
Thanks to Peter Zijlstra for the improved formula!
Signed-off-by: Bruno Randolf <[email protected]>
--
v2: use log2.h functions
---
include/linux/average.h | 4 +---
lib/average.c | 20 ++++++++++++--------
2 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/include/linux/average.h b/include/linux/average.h
index 7706e40..c6028fd 100644
--- a/include/linux/average.h
+++ b/include/linux/average.h
@@ -1,8 +1,6 @@
#ifndef _LINUX_AVERAGE_H
#define _LINUX_AVERAGE_H
-#include <linux/kernel.h>
-
/* Exponentially weighted moving average (EWMA) */
/* For more documentation see lib/average.c */
@@ -26,7 +24,7 @@ extern struct ewma *ewma_add(struct ewma *avg, unsigned long val);
*/
static inline unsigned long ewma_read(const struct ewma *avg)
{
- return DIV_ROUND_CLOSEST(avg->internal, avg->factor);
+ return avg->internal >> avg->factor;
}
#endif /* _LINUX_AVERAGE_H */
diff --git a/lib/average.c b/lib/average.c
index f1d1b46..5576c28 100644
--- a/lib/average.c
+++ b/lib/average.c
@@ -8,6 +8,7 @@
#include <linux/module.h>
#include <linux/average.h>
#include <linux/bug.h>
+#include <linux/log2.h>
/**
* DOC: Exponentially Weighted Moving Average (EWMA)
@@ -24,18 +25,21 @@
* ewma_init() - Initialize EWMA parameters
* @avg: Average structure
* @factor: Factor to use for the scaled up internal value. The maximum value
- * of averages can be ULONG_MAX/(factor*weight).
+ * of averages can be ULONG_MAX/(factor*weight). For performance reasons
+ * factor has to be a power of 2.
* @weight: Exponential weight, or decay rate. This defines how fast the
- * influence of older values decreases. Has to be bigger than 1.
+ * influence of older values decreases. For performance reasons weight has
+ * to be a power of 2.
*
* Initialize the EWMA parameters for a given struct ewma @avg.
*/
void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
{
- WARN_ON(weight <= 1 || factor == 0);
+ WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
+
+ avg->weight = ilog2(weight);
+ avg->factor = ilog2(factor);
avg->internal = 0;
- avg->weight = weight;
- avg->factor = factor;
}
EXPORT_SYMBOL(ewma_init);
@@ -49,9 +53,9 @@ EXPORT_SYMBOL(ewma_init);
struct ewma *ewma_add(struct ewma *avg, unsigned long val)
{
avg->internal = avg->internal ?
- (((avg->internal * (avg->weight - 1)) +
- (val * avg->factor)) / avg->weight) :
- (val * avg->factor);
+ (((avg->internal << avg->weight) - avg->internal) +
+ (val << avg->factor)) >> avg->weight :
+ (val << avg->factor);
return avg;
}
EXPORT_SYMBOL(ewma_add);