xref: /linux-6.15/include/linux/percpu_counter.h (revision 4f3865fb) 
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 */
113