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