/* * 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);