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lib: Improve EWMA efficiency by using bitshifts

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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 <br1@einfach.org>

--

v2:	use log2.h functions
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Bruno Randolf 2010-12-02 19:50:37 +09:00 • committed by John W. Linville
parent 5dcc03fe29
commit af55688435
2 changed files with 13 additions and 11 deletions
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4
include/linux/average.h
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@ -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 */