include/linux/average.h

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