Linux-2.6.12-rc2
[linux-2.6/kvm.git] / include / linux / percpu_counter.h
blobbd6708e2c02703e70be886a4229eb4071be33137
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.
6 * WARNING: these things are HUGE. 4 kbytes per counter on 32-way P4.
7 */
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>
15 #ifdef CONFIG_SMP
17 struct percpu_counter {
18 spinlock_t lock;
19 long count;
20 long *counters;
23 #if NR_CPUS >= 16
24 #define FBC_BATCH (NR_CPUS*2)
25 #else
26 #define FBC_BATCH (NR_CPUS*4)
27 #endif
29 static inline void percpu_counter_init(struct percpu_counter *fbc)
31 spin_lock_init(&fbc->lock);
32 fbc->count = 0;
33 fbc->counters = alloc_percpu(long);
36 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
38 free_percpu(fbc->counters);
41 void percpu_counter_mod(struct percpu_counter *fbc, long amount);
43 static inline long percpu_counter_read(struct percpu_counter *fbc)
45 return fbc->count;
49 * It is possible for the percpu_counter_read() to return a small negative
50 * number for some counter which should never be negative.
52 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
54 long ret = fbc->count;
56 barrier(); /* Prevent reloads of fbc->count */
57 if (ret > 0)
58 return ret;
59 return 1;
62 #else
64 struct percpu_counter {
65 long count;
68 static inline void percpu_counter_init(struct percpu_counter *fbc)
70 fbc->count = 0;
73 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
77 static inline void
78 percpu_counter_mod(struct percpu_counter *fbc, long amount)
80 preempt_disable();
81 fbc->count += amount;
82 preempt_enable();
85 static inline long percpu_counter_read(struct percpu_counter *fbc)
87 return fbc->count;
90 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
92 return fbc->count;
95 #endif /* CONFIG_SMP */
97 static inline void percpu_counter_inc(struct percpu_counter *fbc)
99 percpu_counter_mod(fbc, 1);
102 static inline void percpu_counter_dec(struct percpu_counter *fbc)
104 percpu_counter_mod(fbc, -1);
107 #endif /* _LINUX_PERCPU_COUNTER_H */