Root/lib/atomic64.c

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. <paulus@au1.ibm.com>
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/module.h>
17#include <asm/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    spinlock_t lock;
33    char pad[L1_CACHE_BYTES];
34} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
35
36static inline spinlock_t *lock_addr(const atomic64_t *v)
37{
38    unsigned long addr = (unsigned long) v;
39
40    addr >>= L1_CACHE_SHIFT;
41    addr ^= (addr >> 8) ^ (addr >> 16);
42    return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
43}
44
45long long atomic64_read(const atomic64_t *v)
46{
47    unsigned long flags;
48    spinlock_t *lock = lock_addr(v);
49    long long val;
50
51    spin_lock_irqsave(lock, flags);
52    val = v->counter;
53    spin_unlock_irqrestore(lock, flags);
54    return val;
55}
56EXPORT_SYMBOL(atomic64_read);
57
58void atomic64_set(atomic64_t *v, long long i)
59{
60    unsigned long flags;
61    spinlock_t *lock = lock_addr(v);
62
63    spin_lock_irqsave(lock, flags);
64    v->counter = i;
65    spin_unlock_irqrestore(lock, flags);
66}
67EXPORT_SYMBOL(atomic64_set);
68
69void atomic64_add(long long a, atomic64_t *v)
70{
71    unsigned long flags;
72    spinlock_t *lock = lock_addr(v);
73
74    spin_lock_irqsave(lock, flags);
75    v->counter += a;
76    spin_unlock_irqrestore(lock, flags);
77}
78EXPORT_SYMBOL(atomic64_add);
79
80long long atomic64_add_return(long long a, atomic64_t *v)
81{
82    unsigned long flags;
83    spinlock_t *lock = lock_addr(v);
84    long long val;
85
86    spin_lock_irqsave(lock, flags);
87    val = v->counter += a;
88    spin_unlock_irqrestore(lock, flags);
89    return val;
90}
91EXPORT_SYMBOL(atomic64_add_return);
92
93void atomic64_sub(long long a, atomic64_t *v)
94{
95    unsigned long flags;
96    spinlock_t *lock = lock_addr(v);
97
98    spin_lock_irqsave(lock, flags);
99    v->counter -= a;
100    spin_unlock_irqrestore(lock, flags);
101}
102EXPORT_SYMBOL(atomic64_sub);
103
104long long atomic64_sub_return(long long a, atomic64_t *v)
105{
106    unsigned long flags;
107    spinlock_t *lock = lock_addr(v);
108    long long val;
109
110    spin_lock_irqsave(lock, flags);
111    val = v->counter -= a;
112    spin_unlock_irqrestore(lock, flags);
113    return val;
114}
115EXPORT_SYMBOL(atomic64_sub_return);
116
117long long atomic64_dec_if_positive(atomic64_t *v)
118{
119    unsigned long flags;
120    spinlock_t *lock = lock_addr(v);
121    long long val;
122
123    spin_lock_irqsave(lock, flags);
124    val = v->counter - 1;
125    if (val >= 0)
126        v->counter = val;
127    spin_unlock_irqrestore(lock, flags);
128    return val;
129}
130EXPORT_SYMBOL(atomic64_dec_if_positive);
131
132long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
133{
134    unsigned long flags;
135    spinlock_t *lock = lock_addr(v);
136    long long val;
137
138    spin_lock_irqsave(lock, flags);
139    val = v->counter;
140    if (val == o)
141        v->counter = n;
142    spin_unlock_irqrestore(lock, flags);
143    return val;
144}
145EXPORT_SYMBOL(atomic64_cmpxchg);
146
147long long atomic64_xchg(atomic64_t *v, long long new)
148{
149    unsigned long flags;
150    spinlock_t *lock = lock_addr(v);
151    long long val;
152
153    spin_lock_irqsave(lock, flags);
154    val = v->counter;
155    v->counter = new;
156    spin_unlock_irqrestore(lock, flags);
157    return val;
158}
159EXPORT_SYMBOL(atomic64_xchg);
160
161int atomic64_add_unless(atomic64_t *v, long long a, long long u)
162{
163    unsigned long flags;
164    spinlock_t *lock = lock_addr(v);
165    int ret = 0;
166
167    spin_lock_irqsave(lock, flags);
168    if (v->counter != u) {
169        v->counter += a;
170        ret = 1;
171    }
172    spin_unlock_irqrestore(lock, flags);
173    return ret;
174}
175EXPORT_SYMBOL(atomic64_add_unless);
176
177static int init_atomic64_lock(void)
178{
179    int i;
180
181    for (i = 0; i < NR_LOCKS; ++i)
182        spin_lock_init(&atomic64_lock[i].lock);
183    return 0;
184}
185
186pure_initcall(init_atomic64_lock);
187

Archive Download this file



interactive