include/linux/pcounter.h

   1 #ifndef __LINUX_PCOUNTER_H
   2 #define __LINUX_PCOUNTER_H
   3 /*
   4  * Using a dynamic percpu 'int' variable has a cost :
   5  * 1) Extra dereference
   6  * Current per_cpu_ptr() implementation uses an array per 'percpu variable'.
   7  * 2) memory cost of NR_CPUS*(32+sizeof(void *)) instead of num_possible_cpus()*4
   8  *
   9  * This pcounter implementation is an abstraction to be able to use
  10  * either a static or a dynamic per cpu variable.
  11  * One dynamic per cpu variable gets a fast & cheap implementation, we can
  12  * change pcounter implementation too.
  13  */
  14 struct pcounter {
  15 #ifdef CONFIG_SMP
  16         void            (*add)(struct pcounter *self, int inc);
  17         int             (*getval)(const struct pcounter *self, int cpu);
  18         int             *per_cpu_values;
  19 #else
  20         int             val;
  21 #endif
  22 };
  23
  24 #ifdef CONFIG_SMP
  25 #include <linux/percpu.h>
  26
  27 #define DEFINE_PCOUNTER(NAME)                                           \
  28 static DEFINE_PER_CPU(int, NAME##_pcounter_values);                     \
  29 static void NAME##_pcounter_add(struct pcounter *self, int val)         \
  30 {                                                                       \
  31        __get_cpu_var(NAME##_pcounter_values) += val;                    \
  32 }                                                                       \
  33 static int NAME##_pcounter_getval(const struct pcounter *self, int cpu) \
  34 {                                                                       \
  35         return per_cpu(NAME##_pcounter_values, cpu);                    \
  36 }                                                                       \
  37
  38 #define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER)               \
  39         MEMBER = {                                              \
  40                 .add    = NAME##_pcounter_add,                  \
  41                 .getval = NAME##_pcounter_getval,               \
  42         }
  43
  44
  45 static inline void pcounter_add(struct pcounter *self, int inc)
  46 {
  47         self->add(self, inc);
  48 }
  49
  50 extern int pcounter_getval(const struct pcounter *self);
  51 extern int pcounter_alloc(struct pcounter *self);
  52 extern void pcounter_free(struct pcounter *self);
  53
  54
  55 #else /* CONFIG_SMP */
  56
  57 static inline void pcounter_add(struct pcounter *self, int inc)
  58 {
  59         self->val += inc;
  60 }
  61
  62 static inline int pcounter_getval(const struct pcounter *self)
  63 {
  64         return self->val;
  65 }
  66
  67 #define DEFINE_PCOUNTER(NAME)
  68 #define PCOUNTER_MEMBER_INITIALIZER(NAME, MEMBER)
  69 #define pcounter_alloc(self) 0
  70 #define pcounter_free(self)
  71
  72 #endif /* CONFIG_SMP */
  73
  74 #endif /* __LINUX_PCOUNTER_H */