diff options
author | Bruno Randolf <br1@einfach.org> | 2010-11-16 02:58:37 +0100 |
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committer | John W. Linville <linville@tuxdriver.com> | 2010-11-18 20:21:52 +0100 |
commit | c5485a7e7569ab32eea240c850198519e2a765ef (patch) | |
tree | 928a8556deaec0811d1b83102b33365aab28a270 /lib/average.c | |
parent | mac80211: fix powersaving clients races (diff) | |
download | linux-c5485a7e7569ab32eea240c850198519e2a765ef.tar.xz linux-c5485a7e7569ab32eea240c850198519e2a765ef.zip |
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 <br1@einfach.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Diffstat (limited to 'lib/average.c')
-rw-r--r-- | lib/average.c | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/lib/average.c b/lib/average.c new file mode 100644 index 000000000000..f1d1b4660c42 --- /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 <linux/module.h> +#include <linux/average.h> +#include <linux/bug.h> + +/** + * 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); |