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/config.h>
  10 #include <linux/spinlock.h>
  11 #include <linux/smp.h>
  12 #include <linux/threads.h>
  13 #include <linux/percpu.h>
  14
  15 #ifdef CONFIG_SMP
  16
  17 struct percpu_counter {
  18         spinlock_t lock;
  19         long count;
  20         long *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)
  30 {
  31         spin_lock_init(&fbc->lock);
  32         fbc->count = 0;
  33         fbc->counters = alloc_percpu(long);
  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, long amount);
  42 long percpu_counter_sum(struct percpu_counter *fbc);
  43
  44 static inline long 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 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
  54 {
  55         long ret = fbc->count;
  56
  57         barrier();              /* Prevent reloads of fbc->count */
  58         if (ret > 0)
  59                 return ret;
  60         return 1;
  61 }
  62
  63 #else
  64
  65 struct percpu_counter {
  66         long count;
  67 };
  68
  69 static inline void percpu_counter_init(struct percpu_counter *fbc)
  70 {
  71         fbc->count = 0;
  72 }
  73
  74 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  75 {
  76 }
  77
  78 static inline void
  79 percpu_counter_mod(struct percpu_counter *fbc, long amount)
  80 {
  81         preempt_disable();
  82         fbc->count += amount;
  83         preempt_enable();
  84 }
  85
  86 static inline long percpu_counter_read(struct percpu_counter *fbc)
  87 {
  88         return fbc->count;
  89 }
  90
  91 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
  92 {
  93         return fbc->count;
  94 }
  95
  96 static inline long percpu_counter_sum(struct percpu_counter *fbc)
  97 {
  98         return percpu_counter_read_positive(fbc);
  99 }
 100
 101 #endif  /* CONFIG_SMP */
 102
 103 static inline void percpu_counter_inc(struct percpu_counter *fbc)
 104 {
 105         percpu_counter_mod(fbc, 1);
 106 }
 107
 108 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 109 {
 110         percpu_counter_mod(fbc, -1);
 111 }
 112
 113 #endif /* _LINUX_PERCPU_COUNTER_H */