58 строки
1.7 KiB
C
58 строки
1.7 KiB
C
/*
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* lib/average.c
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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#include <linux/module.h>
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#include <linux/average.h>
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#include <linux/bug.h>
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/**
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* DOC: Exponentially Weighted Moving Average (EWMA)
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*
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* These are generic functions for calculating Exponentially Weighted Moving
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* Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
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* up internal representation of the average value to prevent rounding errors.
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* The factor for scaling up and the exponential weight (or decay rate) have to
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* be specified thru the init fuction. The structure should not be accessed
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* directly but only thru the helper functions.
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*/
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/**
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* ewma_init() - Initialize EWMA parameters
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* @avg: Average structure
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* @factor: Factor to use for the scaled up internal value. The maximum value
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* of averages can be ULONG_MAX/(factor*weight).
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* @weight: Exponential weight, or decay rate. This defines how fast the
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* influence of older values decreases. Has to be bigger than 1.
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*
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* Initialize the EWMA parameters for a given struct ewma @avg.
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*/
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void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
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{
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WARN_ON(weight <= 1 || factor == 0);
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avg->internal = 0;
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avg->weight = weight;
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avg->factor = factor;
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}
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EXPORT_SYMBOL(ewma_init);
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/**
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* ewma_add() - Exponentially weighted moving average (EWMA)
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* @avg: Average structure
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* @val: Current value
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*
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* Add a sample to the average.
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*/
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struct ewma *ewma_add(struct ewma *avg, unsigned long val)
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{
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avg->internal = avg->internal ?
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(((avg->internal * (avg->weight - 1)) +
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(val * avg->factor)) / avg->weight) :
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(val * avg->factor);
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return avg;
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}
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EXPORT_SYMBOL(ewma_add);
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