From c5485a7e7569ab32eea240c850198519e2a765ef Mon Sep 17 00:00:00 2001 From: Bruno Randolf Date: Tue, 16 Nov 2010 10:58:37 +0900 Subject: lib: Add generic exponentially weighted moving average (EWMA) function This adds generic functions for calculating Exponentially Weighted Moving Averages (EWMA). This implementation makes use of a structure which keeps the EWMA parameters and a scaled up internal representation to reduce rounding errors. The original idea for this implementation came from the rt2x00 driver (rt2x00link.c). I would like to use it in several places in the mac80211 and ath5k code and I hope it can be useful in many other places in the kernel code. Signed-off-by: Bruno Randolf Reviewed-by: KOSAKI Motohiro Signed-off-by: John W. Linville --- include/linux/average.h | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) create mode 100644 include/linux/average.h (limited to 'include/linux/average.h') diff --git a/include/linux/average.h b/include/linux/average.h new file mode 100644 index 000000000000..7706e40f95fa --- /dev/null +++ b/include/linux/average.h @@ -0,0 +1,32 @@ +#ifndef _LINUX_AVERAGE_H +#define _LINUX_AVERAGE_H + +#include + +/* Exponentially weighted moving average (EWMA) */ + +/* For more documentation see lib/average.c */ + +struct ewma { + unsigned long internal; + unsigned long factor; + unsigned long weight; +}; + +extern void ewma_init(struct ewma *avg, unsigned long factor, + unsigned long weight); + +extern struct ewma *ewma_add(struct ewma *avg, unsigned long val); + +/** + * ewma_read() - Get average value + * @avg: Average structure + * + * Returns the average value held in @avg. + */ +static inline unsigned long ewma_read(const struct ewma *avg) +{ + return DIV_ROUND_CLOSEST(avg->internal, avg->factor); +} + +#endif /* _LINUX_AVERAGE_H */ -- cgit v1.2.2 From af5568843594fb71055debe36e521fa8072fcecc Mon Sep 17 00:00:00 2001 From: Bruno Randolf Date: Thu, 2 Dec 2010 19:50:37 +0900 Subject: lib: Improve EWMA efficiency by using bitshifts 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 -- v2: use log2.h functions Signed-off-by: John W. Linville --- include/linux/average.h | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'include/linux/average.h') diff --git a/include/linux/average.h b/include/linux/average.h index 7706e40f95fa..c6028fd742c1 100644 --- a/include/linux/average.h +++ b/include/linux/average.h @@ -1,8 +1,6 @@ #ifndef _LINUX_AVERAGE_H #define _LINUX_AVERAGE_H -#include - /* 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 */ -- cgit v1.2.2