xref: /linux-6.15/include/linux/percpu_counter.h (revision aeb3f462) 
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 void percpu_counter_init(struct percpu_counter *fbc, s64 amount);
34 void percpu_counter_destroy(struct percpu_counter *fbc);
35 void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
36 s64 percpu_counter_sum(struct percpu_counter *fbc);
37 
38 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
39 {
40 	return fbc->count;
41 }
42 
43 /*
44  * It is possible for the percpu_counter_read() to return a small negative
45  * number for some counter which should never be negative.
46  *
47  */
48 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
49 {
50 	s64 ret = fbc->count;
51 
52 	barrier();		/* Prevent reloads of fbc->count */
53 	if (ret >= 0)
54 		return ret;
55 	return 1;
56 }
57 
58 #else
59 
60 struct percpu_counter {
61 	s64 count;
62 };
63 
64 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
65 {
66 	fbc->count = amount;
67 }
68 
69 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
70 {
71 }
72 
73 static inline void
74 percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
75 {
76 	preempt_disable();
77 	fbc->count += amount;
78 	preempt_enable();
79 }
80 
81 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
82 {
83 	return fbc->count;
84 }
85 
86 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
87 {
88 	return fbc->count;
89 }
90 
91 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
92 {
93 	return percpu_counter_read_positive(fbc);
94 }
95 
96 #endif	/* CONFIG_SMP */
97 
98 static inline void percpu_counter_inc(struct percpu_counter *fbc)
99 {
100 	percpu_counter_mod(fbc, 1);
101 }
102 
103 static inline void percpu_counter_dec(struct percpu_counter *fbc)
104 {
105 	percpu_counter_mod(fbc, -1);
106 }
107 
108 #endif /* _LINUX_PERCPU_COUNTER_H */
109