include/linux/average.h

   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 */