mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-28 07:04:00 +08:00
03144b5869
To ensure ewma_read() without a lock returns a valid but possibly out of date average, modify ewma_add() by using ACCESS_ONCE to prevent intermediate wrong values from being written to avg->internal. Suggested-by: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Michael Dalton <mwdalton@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
65 lines
1.9 KiB
C
65 lines
1.9 KiB
C
/*
|
|
* 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/export.h>
|
|
#include <linux/average.h>
|
|
#include <linux/kernel.h>
|
|
#include <linux/bug.h>
|
|
#include <linux/log2.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). For performance reasons
|
|
* factor has to be a power of 2.
|
|
* @weight: Exponential weight, or decay rate. This defines how fast the
|
|
* influence of older values decreases. For performance reasons weight has
|
|
* to be a power of 2.
|
|
*
|
|
* Initialize the EWMA parameters for a given struct ewma @avg.
|
|
*/
|
|
void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
|
|
{
|
|
WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
|
|
|
|
avg->weight = ilog2(weight);
|
|
avg->factor = ilog2(factor);
|
|
avg->internal = 0;
|
|
}
|
|
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)
|
|
{
|
|
unsigned long internal = ACCESS_ONCE(avg->internal);
|
|
|
|
ACCESS_ONCE(avg->internal) = internal ?
|
|
(((internal << avg->weight) - internal) +
|
|
(val << avg->factor)) >> avg->weight :
|
|
(val << avg->factor);
|
|
return avg;
|
|
}
|
|
EXPORT_SYMBOL(ewma_add);
|