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 --- lib/Kconfig | 3 +++ lib/Makefile | 2 ++ lib/average.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 62 insertions(+) create mode 100644 lib/average.c (limited to 'lib') diff --git a/lib/Kconfig b/lib/Kconfig index fa9bf2c0619..3116aa631af 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -210,4 +210,7 @@ config GENERIC_ATOMIC64 config LRU_CACHE tristate +config AVERAGE + bool + endmenu diff --git a/lib/Makefile b/lib/Makefile index e6a3763b821..76d3b851490 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -106,6 +106,8 @@ obj-$(CONFIG_GENERIC_ATOMIC64) += atomic64.o obj-$(CONFIG_ATOMIC64_SELFTEST) += atomic64_test.o +obj-$(CONFIG_AVERAGE) += average.o + hostprogs-y := gen_crc32table clean-files := crc32table.h diff --git a/lib/average.c b/lib/average.c new file mode 100644 index 00000000000..f1d1b4660c4 --- /dev/null +++ b/lib/average.c @@ -0,0 +1,57 @@ +/* + * lib/average.c + * + * This source code is licensed under the GNU General Public License, + * Version 2. See the file COPYING for more details. + */ + +#include +#include +#include + +/** + * DOC: Exponentially Weighted Moving Average (EWMA) + * + * These are generic functions for calculating Exponentially Weighted Moving + * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled + * up internal representation of the average value to prevent rounding errors. + * The factor for scaling up and the exponential weight (or decay rate) have to + * be specified thru the init fuction. The structure should not be accessed + * directly but only thru the helper functions. + */ + +/** + * 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). + * @weight: Exponential weight, or decay rate. This defines how fast the + * influence of older values decreases. Has to be bigger than 1. + * + * 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); + avg->internal = 0; + avg->weight = weight; + avg->factor = factor; +} +EXPORT_SYMBOL(ewma_init); + +/** + * ewma_add() - Exponentially weighted moving average (EWMA) + * @avg: Average structure + * @val: Current value + * + * Add a sample to the average. + */ +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); + return avg; +} +EXPORT_SYMBOL(ewma_add); -- cgit v1.2.3