xref: /linux-6.15/include/linux/percpu_counter.h (revision de2fe5e0) 
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 long percpu_counter_sum(struct percpu_counter *fbc);
43 
44 static inline long percpu_counter_read(struct percpu_counter *fbc)
45 {
46 	return fbc->count;
47 }
48 
49 /*
50  * It is possible for the percpu_counter_read() to return a small negative
51  * number for some counter which should never be negative.
52  */
53 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
54 {
55 	long ret = fbc->count;
56 
57 	barrier();		/* Prevent reloads of fbc->count */
58 	if (ret > 0)
59 		return ret;
60 	return 1;
61 }
62 
63 #else
64 
65 struct percpu_counter {
66 	long count;
67 };
68 
69 static inline void percpu_counter_init(struct percpu_counter *fbc)
70 {
71 	fbc->count = 0;
72 }
73 
74 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
75 {
76 }
77 
78 static inline void
79 percpu_counter_mod(struct percpu_counter *fbc, long amount)
80 {
81 	preempt_disable();
82 	fbc->count += amount;
83 	preempt_enable();
84 }
85 
86 static inline long percpu_counter_read(struct percpu_counter *fbc)
87 {
88 	return fbc->count;
89 }
90 
91 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
92 {
93 	return fbc->count;
94 }
95 
96 static inline long percpu_counter_sum(struct percpu_counter *fbc)
97 {
98 	return percpu_counter_read_positive(fbc);
99 }
100 
101 #endif	/* CONFIG_SMP */
102 
103 static inline void percpu_counter_inc(struct percpu_counter *fbc)
104 {
105 	percpu_counter_mod(fbc, 1);
106 }
107 
108 static inline void percpu_counter_dec(struct percpu_counter *fbc)
109 {
110 	percpu_counter_mod(fbc, -1);
111 }
112 
113 #endif /* _LINUX_PERCPU_COUNTER_H */
114