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
  14 #ifdef CONFIG_SMP
  15
  16 struct percpu_counter {
  17         spinlock_t lock;
  18         long count;
  19         long *counters;
  20 };
  21
  22 #if NR_CPUS >= 16
  23 #define FBC_BATCH       (NR_CPUS*2)
  24 #else
  25 #define FBC_BATCH       (NR_CPUS*4)
  26 #endif
  27
  28 static inline void percpu_counter_init(struct percpu_counter *fbc)
  29 {
  30         spin_lock_init(&fbc->lock);
  31         fbc->count = 0;
  32         fbc->counters = alloc_percpu(long);
  33 }
  34
  35 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  36 {
  37         free_percpu(fbc->counters);
  38 }
  39
  40 void percpu_counter_mod(struct percpu_counter *fbc, long amount);
  41 long percpu_counter_sum(struct percpu_counter *fbc);
  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 static inline long percpu_counter_sum(struct percpu_counter *fbc)
  96 {
  97         return percpu_counter_read_positive(fbc);
  98 }
  99
 100 #endif  /* CONFIG_SMP */
 101
 102 static inline void percpu_counter_inc(struct percpu_counter *fbc)
 103 {
 104         percpu_counter_mod(fbc, 1);
 105 }
 106
 107 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 108 {
 109         percpu_counter_mod(fbc, -1);
 110 }
 111
 112 #endif /* _LINUX_PERCPU_COUNTER_H */