include/linux/average.h

   1 #ifndef _LINUX_AVERAGE_H
   2 #define _LINUX_AVERAGE_H
   3
   4 /* Exponentially weighted moving average (EWMA) */
   5
   6 /* For more documentation see lib/average.c */
   7
   8 struct ewma {
   9         unsigned long internal;
  10         unsigned long factor;
  11         unsigned long weight;
  12 };
  13
  14 extern void ewma_init(struct ewma *avg, unsigned long factor,
  15                       unsigned long weight);
  16
  17 extern struct ewma *ewma_add(struct ewma *avg, unsigned long val);
  18
  19 /**
  20  * ewma_read() - Get average value
  21  * @avg: Average structure
  22  *
  23  * Returns the average value held in @avg.
  24  */
  25 static inline unsigned long ewma_read(const struct ewma *avg)
  26 {
  27         return avg->internal >> avg->factor;
  28 }
  29
  30 #define DECLARE_EWMA(name, _factor, _weight)                            \
  31         struct ewma_##name {                                            \
  32                 unsigned long internal;                                 \
  33         };                                                              \
  34         static inline void ewma_##name##_init(struct ewma_##name *e)    \
  35         {                                                               \
  36                 BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
  37                 BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
  38                 BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
  39                 BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
  40                 e->internal = 0;                                        \
  41         }                                                               \
  42         static inline unsigned long                                     \
  43         ewma_##name##_read(struct ewma_##name *e)                       \
  44         {                                                               \
  45                 BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
  46                 BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
  47                 BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
  48                 BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
  49                 return e->internal >> ilog2(_factor);                   \
  50         }                                                               \
  51         static inline void ewma_##name##_add(struct ewma_##name *e,     \
  52                                              unsigned long val)         \
  53         {                                                               \
  54                 unsigned long internal = ACCESS_ONCE(e->internal);      \
  55                 unsigned long weight = ilog2(_weight);                  \
  56                 unsigned long factor = ilog2(_factor);                  \
  57                                                                         \
  58                 BUILD_BUG_ON(!__builtin_constant_p(_factor));           \
  59                 BUILD_BUG_ON(!__builtin_constant_p(_weight));           \
  60                 BUILD_BUG_ON_NOT_POWER_OF_2(_factor);                   \
  61                 BUILD_BUG_ON_NOT_POWER_OF_2(_weight);                   \
  62                                                                         \
  63                 ACCESS_ONCE(e->internal) = internal ?                   \
  64                         (((internal << weight) - internal) +            \
  65                                 (val << factor)) >> weight :            \
  66                         (val << factor);                                \
  67         }
  68
  69 #endif /* _LINUX_AVERAGE_H */