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 int percpu_counter_init(struct percpu_counter *fbc, s64 amount);
  34 int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
  35 void percpu_counter_destroy(struct percpu_counter *fbc);
  36 void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
  37 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
  38 s64 __percpu_counter_sum(struct percpu_counter *fbc);
  39
  40 static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
  41 {
  42         __percpu_counter_add(fbc, amount, FBC_BATCH);
  43 }
  44
  45 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
  46 {
  47         s64 ret = __percpu_counter_sum(fbc);
  48         return ret < 0 ? 0 : ret;
  49 }
  50
  51 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
  52 {
  53         return __percpu_counter_sum(fbc);
  54 }
  55
  56 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  57 {
  58         return fbc->count;
  59 }
  60
  61 /*
  62  * It is possible for the percpu_counter_read() to return a small negative
  63  * number for some counter which should never be negative.
  64  *
  65  */
  66 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  67 {
  68         s64 ret = fbc->count;
  69
  70         barrier();              /* Prevent reloads of fbc->count */
  71         if (ret >= 0)
  72                 return ret;
  73         return 1;
  74 }
  75
  76 #else
  77
  78 struct percpu_counter {
  79         s64 count;
  80 };
  81
  82 static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount)
  83 {
  84         fbc->count = amount;
  85         return 0;
  86 }
  87
  88 #define percpu_counter_init_irq percpu_counter_init
  89
  90 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
  91 {
  92 }
  93
  94 static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
  95 {
  96         fbc->count = amount;
  97 }
  98
  99 #define __percpu_counter_add(fbc, amount, batch) \
 100         percpu_counter_add(fbc, amount)
 101
 102 static inline void
 103 percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 104 {
 105         preempt_disable();
 106         fbc->count += amount;
 107         preempt_enable();
 108 }
 109
 110 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
 111 {
 112         return fbc->count;
 113 }
 114
 115 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
 116 {
 117         return fbc->count;
 118 }
 119
 120 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
 121 {
 122         return percpu_counter_read_positive(fbc);
 123 }
 124
 125 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
 126 {
 127         return percpu_counter_read(fbc);
 128 }
 129
 130 #endif  /* CONFIG_SMP */
 131
 132 static inline void percpu_counter_inc(struct percpu_counter *fbc)
 133 {
 134         percpu_counter_add(fbc, 1);
 135 }
 136
 137 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 138 {
 139         percpu_counter_add(fbc, -1);
 140 }
 141
 142 static inline void percpu_counter_sub(struct percpu_counter *fbc, s64 amount)
 143 {
 144         percpu_counter_add(fbc, -amount);
 145 }
 146
 147 #endif /* _LINUX_PERCPU_COUNTER_H */