include/linux/average.h

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