projects/linux·blob v4.6 · refs

171 lines · 4.1 KiB

1/*
2 * Generic implementation of 64-bit atomics using spinlocks,
3 * useful on processors that don't have 64-bit atomic instructions.
4 *
5 * Copyright © 2009 Paul Mackerras, IBM Corp. <[email protected]>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version
10 * 2 of the License, or (at your option) any later version.
11 */
12#include <linux/types.h>
13#include <linux/cache.h>
14#include <linux/spinlock.h>
15#include <linux/init.h>
16#include <linux/export.h>
17#include <linux/atomic.h>
18
19/*
20 * We use a hashed array of spinlocks to provide exclusive access
21 * to each atomic64_t variable. Since this is expected to used on
22 * systems with small numbers of CPUs (<= 4 or so), we use a
23 * relatively small array of 16 spinlocks to avoid wasting too much
24 * memory on the spinlock array.
25 */
26#define NR_LOCKS 16
27
28/*
29 * Ensure each lock is in a separate cacheline.
30 */
31static union {
32 raw_spinlock_t lock;
33 char pad[L1_CACHE_BYTES];
34} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp = {
35 [0 ... (NR_LOCKS - 1)] = {
36 .lock = __RAW_SPIN_LOCK_UNLOCKED(atomic64_lock.lock),
37 },
38};
39
40static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
41{
42 unsigned long addr = (unsigned long) v;
43
44 addr >>= L1_CACHE_SHIFT;
45 addr ^= (addr >> 8) ^ (addr >> 16);
46 return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
47}
48
49long long atomic64_read(const atomic64_t *v)
50{
51 unsigned long flags;
52 raw_spinlock_t *lock = lock_addr(v);
53 long long val;
54
55 raw_spin_lock_irqsave(lock, flags);
56 val = v->counter;
57 raw_spin_unlock_irqrestore(lock, flags);
58 return val;
59}
60EXPORT_SYMBOL(atomic64_read);
61
62void atomic64_set(atomic64_t *v, long long i)
63{
64 unsigned long flags;
65 raw_spinlock_t *lock = lock_addr(v);
66
67 raw_spin_lock_irqsave(lock, flags);
68 v->counter = i;
69 raw_spin_unlock_irqrestore(lock, flags);
70}
71EXPORT_SYMBOL(atomic64_set);
72
73#define ATOMIC64_OP(op, c_op) \
74void atomic64_##op(long long a, atomic64_t *v) \
75{ \
76 unsigned long flags; \
77 raw_spinlock_t *lock = lock_addr(v); \
78 \
79 raw_spin_lock_irqsave(lock, flags); \
80 v->counter c_op a; \
81 raw_spin_unlock_irqrestore(lock, flags); \
82} \
83EXPORT_SYMBOL(atomic64_##op);
84
85#define ATOMIC64_OP_RETURN(op, c_op) \
86long long atomic64_##op##_return(long long a, atomic64_t *v) \
87{ \
88 unsigned long flags; \
89 raw_spinlock_t *lock = lock_addr(v); \
90 long long val; \
91 \
92 raw_spin_lock_irqsave(lock, flags); \
93 val = (v->counter c_op a); \
94 raw_spin_unlock_irqrestore(lock, flags); \
95 return val; \
96} \
97EXPORT_SYMBOL(atomic64_##op##_return);
98
99#define ATOMIC64_OPS(op, c_op) \
100 ATOMIC64_OP(op, c_op) \
101 ATOMIC64_OP_RETURN(op, c_op)
102
103ATOMIC64_OPS(add, +=)
104ATOMIC64_OPS(sub, -=)
105ATOMIC64_OP(and, &=)
106ATOMIC64_OP(or, |=)
107ATOMIC64_OP(xor, ^=)
108
109#undef ATOMIC64_OPS
110#undef ATOMIC64_OP_RETURN
111#undef ATOMIC64_OP
112
113long long atomic64_dec_if_positive(atomic64_t *v)
114{
115 unsigned long flags;
116 raw_spinlock_t *lock = lock_addr(v);
117 long long val;
118
119 raw_spin_lock_irqsave(lock, flags);
120 val = v->counter - 1;
121 if (val >= 0)
122 v->counter = val;
123 raw_spin_unlock_irqrestore(lock, flags);
124 return val;
125}
126EXPORT_SYMBOL(atomic64_dec_if_positive);
127
128long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
129{
130 unsigned long flags;
131 raw_spinlock_t *lock = lock_addr(v);
132 long long val;
133
134 raw_spin_lock_irqsave(lock, flags);
135 val = v->counter;
136 if (val == o)
137 v->counter = n;
138 raw_spin_unlock_irqrestore(lock, flags);
139 return val;
140}
141EXPORT_SYMBOL(atomic64_cmpxchg);
142
143long long atomic64_xchg(atomic64_t *v, long long new)
144{
145 unsigned long flags;
146 raw_spinlock_t *lock = lock_addr(v);
147 long long val;
148
149 raw_spin_lock_irqsave(lock, flags);
150 val = v->counter;
151 v->counter = new;
152 raw_spin_unlock_irqrestore(lock, flags);
153 return val;
154}
155EXPORT_SYMBOL(atomic64_xchg);
156
157int atomic64_add_unless(atomic64_t *v, long long a, long long u)
158{
159 unsigned long flags;
160 raw_spinlock_t *lock = lock_addr(v);
161 int ret = 0;
162
163 raw_spin_lock_irqsave(lock, flags);
164 if (v->counter != u) {
165 v->counter += a;
166 ret = 1;
167 }
168 raw_spin_unlock_irqrestore(lock, flags);
169 return ret;
170}
171EXPORT_SYMBOL(atomic64_add_unless);