1*4882a593Smuzhiyun /* SPDX-License-Identifier: GPL-2.0 */ 2*4882a593Smuzhiyun #ifndef _LINUX_AVERAGE_H 3*4882a593Smuzhiyun #define _LINUX_AVERAGE_H 4*4882a593Smuzhiyun 5*4882a593Smuzhiyun #include <linux/bug.h> 6*4882a593Smuzhiyun #include <linux/compiler.h> 7*4882a593Smuzhiyun #include <linux/log2.h> 8*4882a593Smuzhiyun 9*4882a593Smuzhiyun /* 10*4882a593Smuzhiyun * Exponentially weighted moving average (EWMA) 11*4882a593Smuzhiyun * 12*4882a593Smuzhiyun * This implements a fixed-precision EWMA algorithm, with both the 13*4882a593Smuzhiyun * precision and fall-off coefficient determined at compile-time 14*4882a593Smuzhiyun * and built into the generated helper funtions. 15*4882a593Smuzhiyun * 16*4882a593Smuzhiyun * The first argument to the macro is the name that will be used 17*4882a593Smuzhiyun * for the struct and helper functions. 18*4882a593Smuzhiyun * 19*4882a593Smuzhiyun * The second argument, the precision, expresses how many bits are 20*4882a593Smuzhiyun * used for the fractional part of the fixed-precision values. 21*4882a593Smuzhiyun * 22*4882a593Smuzhiyun * The third argument, the weight reciprocal, determines how the 23*4882a593Smuzhiyun * new values will be weighed vs. the old state, new values will 24*4882a593Smuzhiyun * get weight 1/weight_rcp and old values 1-1/weight_rcp. Note 25*4882a593Smuzhiyun * that this parameter must be a power of two for efficiency. 26*4882a593Smuzhiyun */ 27*4882a593Smuzhiyun 28*4882a593Smuzhiyun #define DECLARE_EWMA(name, _precision, _weight_rcp) \ 29*4882a593Smuzhiyun struct ewma_##name { \ 30*4882a593Smuzhiyun unsigned long internal; \ 31*4882a593Smuzhiyun }; \ 32*4882a593Smuzhiyun static inline void ewma_##name##_init(struct ewma_##name *e) \ 33*4882a593Smuzhiyun { \ 34*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_precision)); \ 35*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \ 36*4882a593Smuzhiyun /* \ 37*4882a593Smuzhiyun * Even if you want to feed it just 0/1 you should have \ 38*4882a593Smuzhiyun * some bits for the non-fractional part... \ 39*4882a593Smuzhiyun */ \ 40*4882a593Smuzhiyun BUILD_BUG_ON((_precision) > 30); \ 41*4882a593Smuzhiyun BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \ 42*4882a593Smuzhiyun e->internal = 0; \ 43*4882a593Smuzhiyun } \ 44*4882a593Smuzhiyun static inline unsigned long \ 45*4882a593Smuzhiyun ewma_##name##_read(struct ewma_##name *e) \ 46*4882a593Smuzhiyun { \ 47*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_precision)); \ 48*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \ 49*4882a593Smuzhiyun BUILD_BUG_ON((_precision) > 30); \ 50*4882a593Smuzhiyun BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \ 51*4882a593Smuzhiyun return e->internal >> (_precision); \ 52*4882a593Smuzhiyun } \ 53*4882a593Smuzhiyun static inline void ewma_##name##_add(struct ewma_##name *e, \ 54*4882a593Smuzhiyun unsigned long val) \ 55*4882a593Smuzhiyun { \ 56*4882a593Smuzhiyun unsigned long internal = READ_ONCE(e->internal); \ 57*4882a593Smuzhiyun unsigned long weight_rcp = ilog2(_weight_rcp); \ 58*4882a593Smuzhiyun unsigned long precision = _precision; \ 59*4882a593Smuzhiyun \ 60*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_precision)); \ 61*4882a593Smuzhiyun BUILD_BUG_ON(!__builtin_constant_p(_weight_rcp)); \ 62*4882a593Smuzhiyun BUILD_BUG_ON((_precision) > 30); \ 63*4882a593Smuzhiyun BUILD_BUG_ON_NOT_POWER_OF_2(_weight_rcp); \ 64*4882a593Smuzhiyun \ 65*4882a593Smuzhiyun WRITE_ONCE(e->internal, internal ? \ 66*4882a593Smuzhiyun (((internal << weight_rcp) - internal) + \ 67*4882a593Smuzhiyun (val << precision)) >> weight_rcp : \ 68*4882a593Smuzhiyun (val << precision)); \ 69*4882a593Smuzhiyun } 70*4882a593Smuzhiyun 71*4882a593Smuzhiyun #endif /* _LINUX_AVERAGE_H */ 72