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1/* SPDX-License-Identifier: GPL-2.0 */2#ifndef _LINUX_AVERAGE_H3#define _LINUX_AVERAGE_H4 5#include <linux/bug.h>6#include <linux/compiler.h>7#include <linux/log2.h>8 9/*10 * Exponentially weighted moving average (EWMA)11 *12 * This implements a fixed-precision EWMA algorithm, with both the13 * precision and fall-off coefficient determined at compile-time14 * and built into the generated helper funtions.15 *16 * The first argument to the macro is the name that will be used17 * for the struct and helper functions.18 *19 * The second argument, the precision, expresses how many bits are20 * used for the fractional part of the fixed-precision values.21 *22 * The third argument, the weight reciprocal, determines how the23 * new values will be weighed vs. the old state, new values will24 * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note25 * that this parameter must be a power of two for efficiency.26 */27 28#define DECLARE_EWMA(name, _precision, _weight_rcp) \29 struct ewma_##name { \30 unsigned long internal; \31 }; \32 static inline void ewma_##name##_init(struct ewma_##name *e) \33 { \34 BUILD_BUG_ON(!__builtin_constant_p(_precision)); \35 BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \36 /* \37 * Even if you want to feed it just 0/1 you should have \38 * some bits for the non-fractional part... \39 */ \40 BUILD_BUG_ON((_precision) > 30); \41 BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \42 e->internal = 0; \43 } \44 static inline unsigned long \45 ewma_##name##_read(struct ewma_##name *e) \46 { \47 BUILD_BUG_ON(!__builtin_constant_p(_precision)); \48 BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \49 BUILD_BUG_ON((_precision) > 30); \50 BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \51 return e->internal >> (_precision); \52 } \53 static inline void ewma_##name##_add(struct ewma_##name *e, \54 unsigned long val) \55 { \56 unsigned long internal = READ_ONCE(e->internal); \57 unsigned long weight_rcp = ilog2(_weight_rcp); \58 unsigned long precision = _precision; \59 \60 BUILD_BUG_ON(!__builtin_constant_p(_precision)); \61 BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \62 BUILD_BUG_ON((_precision) > 30); \63 BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \64 \65 WRITE_ONCE(e->internal, internal ? \66 (((internal << weight_rcp) - internal) + \67 (val << precision)) >> weight_rcp : \68 (val << precision)); \69 }70 71#endif /* _LINUX_AVERAGE_H */72