2 * Generic implementation of 64-bit atomics using spinlocks,
3 * useful on processors that don't have 64-bit atomic instructions.
5 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
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.
12 #include <linux/types.h>
13 #include <linux/cache.h>
14 #include <linux/spinlock.h>
15 #include <linux/init.h>
16 #include <asm/atomic.h>
19 * We use a hashed array of spinlocks to provide exclusive access
20 * to each atomic64_t variable. Since this is expected to used on
21 * systems with small numbers of CPUs (<= 4 or so), we use a
22 * relatively small array of 16 spinlocks to avoid wasting too much
23 * memory on the spinlock array.
28 * Ensure each lock is in a separate cacheline.
32 char pad
[L1_CACHE_BYTES
];
33 } atomic64_lock
[NR_LOCKS
] __cacheline_aligned_in_smp
;
35 static inline spinlock_t
*lock_addr(const atomic64_t
*v
)
37 unsigned long addr
= (unsigned long) v
;
39 addr
>>= L1_CACHE_SHIFT
;
40 addr
^= (addr
>> 8) ^ (addr
>> 16);
41 return &atomic64_lock
[addr
& (NR_LOCKS
- 1)].lock
;
44 long long atomic64_read(const atomic64_t
*v
)
47 spinlock_t
*lock
= lock_addr(v
);
50 spin_lock_irqsave(lock
, flags
);
52 spin_unlock_irqrestore(lock
, flags
);
56 void atomic64_set(atomic64_t
*v
, long long i
)
59 spinlock_t
*lock
= lock_addr(v
);
61 spin_lock_irqsave(lock
, flags
);
63 spin_unlock_irqrestore(lock
, flags
);
66 void atomic64_add(long long a
, atomic64_t
*v
)
69 spinlock_t
*lock
= lock_addr(v
);
71 spin_lock_irqsave(lock
, flags
);
73 spin_unlock_irqrestore(lock
, flags
);
76 long long atomic64_add_return(long long a
, atomic64_t
*v
)
79 spinlock_t
*lock
= lock_addr(v
);
82 spin_lock_irqsave(lock
, flags
);
83 val
= v
->counter
+= a
;
84 spin_unlock_irqrestore(lock
, flags
);
88 void atomic64_sub(long long a
, atomic64_t
*v
)
91 spinlock_t
*lock
= lock_addr(v
);
93 spin_lock_irqsave(lock
, flags
);
95 spin_unlock_irqrestore(lock
, flags
);
98 long long atomic64_sub_return(long long a
, atomic64_t
*v
)
101 spinlock_t
*lock
= lock_addr(v
);
104 spin_lock_irqsave(lock
, flags
);
105 val
= v
->counter
-= a
;
106 spin_unlock_irqrestore(lock
, flags
);
110 long long atomic64_dec_if_positive(atomic64_t
*v
)
113 spinlock_t
*lock
= lock_addr(v
);
116 spin_lock_irqsave(lock
, flags
);
117 val
= v
->counter
- 1;
120 spin_unlock_irqrestore(lock
, flags
);
124 long long atomic64_cmpxchg(atomic64_t
*v
, long long o
, long long n
)
127 spinlock_t
*lock
= lock_addr(v
);
130 spin_lock_irqsave(lock
, flags
);
134 spin_unlock_irqrestore(lock
, flags
);
138 long long atomic64_xchg(atomic64_t
*v
, long long new)
141 spinlock_t
*lock
= lock_addr(v
);
144 spin_lock_irqsave(lock
, flags
);
147 spin_unlock_irqrestore(lock
, flags
);
151 int atomic64_add_unless(atomic64_t
*v
, long long a
, long long u
)
154 spinlock_t
*lock
= lock_addr(v
);
157 spin_lock_irqsave(lock
, flags
);
158 if (v
->counter
!= u
) {
162 spin_unlock_irqrestore(lock
, flags
);
166 static int init_atomic64_lock(void)
170 for (i
= 0; i
< NR_LOCKS
; ++i
)
171 spin_lock_init(&atomic64_lock
[i
].lock
);
175 pure_initcall(init_atomic64_lock
);