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Commit c5485a7e authored by Bruno Randolf's avatar Bruno Randolf Committed by John W. Linville
Browse files

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: default avatarBruno Randolf <br1@einfach.org>
Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent 50a9432d

include/linux/average.h

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#ifndef _LINUX_AVERAGE_H

#define _LINUX_AVERAGE_H



#include <linux/kernel.h>



/* 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 */

lib/Kconfig

+3 −0
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@@ -210,4 +210,7 @@ config GENERIC_ATOMIC64 
config LRU_CACHE

	tristate



config AVERAGE

	bool



endmenu

lib/Makefile

+2 −0
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@@ -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

lib/average.c

0 → 100644
+57 −0
Original line number Diff line number Diff line 
/*

 * 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);