include/linux/percpu_counter.h

   1 #ifndef _LINUX_PERCPU_COUNTER_H
   2 #define _LINUX_PERCPU_COUNTER_H
   3 /*
   4  * A simple "approximate counter" for use in ext2 and ext3 superblocks.
   5  *
   6  * WARNING: these things are HUGE.  4 kbytes per counter on 32-way P4.
   7  */
   8
   9 #include <linux/spinlock.h>
  10 #include <linux/smp.h>
  11 #include <linux/list.h>
  12 #include <linux/threads.h>
  13 #include <linux/percpu.h>
  14 #include <linux/types.h>
  15
  16 #ifdef CONFIG_SMP
  17
  18 struct percpu_counter {
  19         spinlock_t lock;
  20         s64 count;
  21 #ifdef CONFIG_HOTPLUG_CPU
  22         struct list_head list;  /* All percpu_counters are on a list */
  23 #endif
  24         s32 *counters;
  25 };
  26
  27 #if NR_CPUS >= 16
  28 #define FBC_BATCH       (NR_CPUS*2)
  29 #else
  30 #define FBC_BATCH       (NR_CPUS*4)
  31 #endif
  32
  33 void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
  34 void percpu_counter_destroy(struct percpu_counter *fbc);
  35 void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
  36 s64 percpu_counter_sum(struct percpu_counter *fbc);
  37
  38 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  39 {
  40         return fbc->count;
  41 }
  42
  43 /*
  44  * It is possible for the percpu_counter_read() to return a small negative
  45  * number for some counter which should never be negative.
  46  *
  47  */
  48 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  49 {
  50         s64 ret = fbc->count;
  51
  52         barrier();              /* Prevent reloads of fbc->count */
  53         if (ret >= 0)
  54                 return ret;
  55         return 1;
  56 }
  57
  58 #else
  59
  60 struct percpu_counter {
  61         s64 count;
  62 };
  63
  64 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
  65 {
  66         fbc->count = amount;
  67 }
  68
  69 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  70 {
  71 }
  72
  73 static inline void
  74 percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
  75 {
  76         preempt_disable();
  77         fbc->count += amount;
  78         preempt_enable();
  79 }
  80
  81 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  82 {
  83         return fbc->count;
  84 }
  85
  86 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  87 {
  88         return fbc->count;
  89 }
  90
  91 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
  92 {
  93         return percpu_counter_read_positive(fbc);
  94 }
  95
  96 #endif  /* CONFIG_SMP */
  97
  98 static inline void percpu_counter_inc(struct percpu_counter *fbc)
  99 {
 100         percpu_counter_mod(fbc, 1);
 101 }
 102
 103 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 104 {
 105         percpu_counter_mod(fbc, -1);
 106 }
 107
 108 #endif /* _LINUX_PERCPU_COUNTER_H */