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 | |