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
  43 static inline long percpu_counter_read(struct percpu_counter *fbc)
  44 {
  45         return fbc->count;
  46 }
  47
  48 /*
  49  * It is possible for the percpu_counter_read() to return a small negative
  50  * number for some counter which should never be negative.
  51  */
  52 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
  53 {
  54         long ret = fbc->count;
  55
  56         barrier();              /* Prevent reloads of fbc->count */
  57         if (ret > 0)
  58                 return ret;
  59         return 1;
  60 }
  61
  62 #else
  63
  64 struct percpu_counter {
  65         long count;
  66 };
  67
  68 static inline void percpu_counter_init(struct percpu_counter *fbc)
  69 {
  70         fbc->count = 0;
  71 }
  72
  73 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  74 {
  75 }
  76
  77 static inline void
  78 percpu_counter_mod(struct percpu_counter *fbc, long amount)
  79 {
  80         preempt_disable();
  81         fbc->count += amount;
  82         preempt_enable();
  83 }
  84
  85 static inline long percpu_counter_read(struct percpu_counter *fbc)
  86 {
  87         return fbc->count;
  88 }
  89
  90 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
  91 {
  92         return fbc->count;
  93 }
  94
  95 #endif  /* CONFIG_SMP */
  96
  97 static inline void percpu_counter_inc(struct percpu_counter *fbc)
  98 {
  99         percpu_counter_mod(fbc, 1);
 100 }
 101
 102 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 103 {
 104         percpu_counter_mod(fbc, -1);
 105 }
 106
 107 #endif /* _LINUX_PERCPU_COUNTER_H */