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/threads.h>
  12 #include <linux/percpu.h>
  13 #include <linux/types.h>
  14
  15 #ifdef CONFIG_SMP
  16
  17 struct percpu_counter {
  18         spinlock_t lock;
  19         s64 count;
  20         s32 *counters;
  21 };
  22
  23 #if NR_CPUS >= 16
  24 #define FBC_BATCH       (NR_CPUS*2)
  25 #else
  26 #define FBC_BATCH       (NR_CPUS*4)
  27 #endif
  28
  29 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
  30 {
  31         spin_lock_init(&fbc->lock);
  32         fbc->count = amount;
  33         fbc->counters = alloc_percpu(s32);
  34 }
  35
  36 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  37 {
  38         free_percpu(fbc->counters);
  39 }
  40
  41 void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
  42 s64 percpu_counter_sum(struct percpu_counter *fbc);
  43
  44 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  45 {
  46         return fbc->count;
  47 }
  48
  49 /*
  50  * It is possible for the percpu_counter_read() to return a small negative
  51  * number for some counter which should never be negative.
  52  *
  53  */
  54 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  55 {
  56         s64 ret = fbc->count;
  57
  58         barrier();              /* Prevent reloads of fbc->count */
  59         if (ret >= 0)
  60                 return ret;
  61         return 1;
  62 }
  63
  64 #else
  65
  66 struct percpu_counter {
  67         s64 count;
  68 };
  69
  70 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
  71 {
  72         fbc->count = amount;
  73 }
  74
  75 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  76 {
  77 }
  78
  79 static inline void
  80 percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
  81 {
  82         preempt_disable();
  83         fbc->count += amount;
  84         preempt_enable();
  85 }
  86
  87 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  88 {
  89         return fbc->count;
  90 }
  91
  92 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  93 {
  94         return fbc->count;
  95 }
  96
  97 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
  98 {
  99         return percpu_counter_read_positive(fbc);
 100 }
 101
 102 #endif  /* CONFIG_SMP */
 103
 104 static inline void percpu_counter_inc(struct percpu_counter *fbc)
 105 {
 106         percpu_counter_mod(fbc, 1);
 107 }
 108
 109 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 110 {
 111         percpu_counter_mod(fbc, -1);
 112 }
 113
 114 #endif /* _LINUX_PERCPU_COUNTER_H */