1 /* 2 * lib/average.c 3 * 4 * This source code is licensed under the GNU General Public License, 5 * Version 2. See the file COPYING for more details. 6 */ 7 8 #include <linux/export.h> 9 #include <linux/average.h> 10 #include <linux/kernel.h> 11 #include <linux/bug.h> 12 #include <linux/log2.h> 13 14 /** 15 * DOC: Exponentially Weighted Moving Average (EWMA) 16 * 17 * These are generic functions for calculating Exponentially Weighted Moving 18 * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled 19 * up internal representation of the average value to prevent rounding errors. 20 * The factor for scaling up and the exponential weight (or decay rate) have to 21 * be specified thru the init fuction. The structure should not be accessed 22 * directly but only thru the helper functions. 23 */ 24 25 /** 26 * ewma_init() - Initialize EWMA parameters 27 * @avg: Average structure 28 * @factor: Factor to use for the scaled up internal value. The maximum value 29 * of averages can be ULONG_MAX/(factor*weight). For performance reasons 30 * factor has to be a power of 2. 31 * @weight: Exponential weight, or decay rate. This defines how fast the 32 * influence of older values decreases. For performance reasons weight has 33 * to be a power of 2. 34 * 35 * Initialize the EWMA parameters for a given struct ewma @avg. 36 */ ewma_init(struct ewma * avg,unsigned long factor,unsigned long weight)37void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight) 38 { 39 WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor)); 40 41 avg->weight = ilog2(weight); 42 avg->factor = ilog2(factor); 43 avg->internal = 0; 44 } 45 EXPORT_SYMBOL(ewma_init); 46 47 /** 48 * ewma_add() - Exponentially weighted moving average (EWMA) 49 * @avg: Average structure 50 * @val: Current value 51 * 52 * Add a sample to the average. 53 */ ewma_add(struct ewma * avg,unsigned long val)54struct ewma *ewma_add(struct ewma *avg, unsigned long val) 55 { 56 unsigned long internal = ACCESS_ONCE(avg->internal); 57 58 ACCESS_ONCE(avg->internal) = internal ? 59 (((internal << avg->weight) - internal) + 60 (val << avg->factor)) >> avg->weight : 61 (val << avg->factor); 62 return avg; 63 } 64 EXPORT_SYMBOL(ewma_add); 65