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 */
108
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