1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_AVERAGE_H 3 #define _LINUX_AVERAGE_H 4 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 the 13 * precision and fall-off coefficient determined at compile-time 14 * and built into the generated helper funtions. 15 * 16 * The first argument to the macro is the name that will be used 17 * for the struct and helper functions. 18 * 19 * The second argument, the precision, expresses how many bits are 20 * used for the fractional part of the fixed-precision values. 21 * 22 * The third argument, the weight reciprocal, determines how the 23 * new values will be weighed vs. the old state, new values will 24 * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note 25 * 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