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