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Diffstat (limited to 'lib/atomic64.c')
| -rw-r--r-- | lib/atomic64.c | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/lib/atomic64.c b/lib/atomic64.c new file mode 100644 index 000000000000..c5e725562416 --- /dev/null +++ b/lib/atomic64.c @@ -0,0 +1,175 @@ +/* + * Generic implementation of 64-bit atomics using spinlocks, + * useful on processors that don't have 64-bit atomic instructions. + * + * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + */ +#include <linux/types.h> +#include <linux/cache.h> +#include <linux/spinlock.h> +#include <linux/init.h> +#include <asm/atomic.h> + +/* + * We use a hashed array of spinlocks to provide exclusive access + * to each atomic64_t variable. Since this is expected to used on + * systems with small numbers of CPUs (<= 4 or so), we use a + * relatively small array of 16 spinlocks to avoid wasting too much + * memory on the spinlock array. + */ +#define NR_LOCKS 16 + +/* + * Ensure each lock is in a separate cacheline. + */ +static union { + spinlock_t lock; + char pad[L1_CACHE_BYTES]; +} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp; + +static inline spinlock_t *lock_addr(const atomic64_t *v) +{ + unsigned long addr = (unsigned long) v; + + addr >>= L1_CACHE_SHIFT; + addr ^= (addr >> 8) ^ (addr >> 16); + return &atomic64_lock[addr & (NR_LOCKS - 1)].lock; +} + +long long atomic64_read(const atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter; + spin_unlock_irqrestore(lock, flags); + return val; +} + +void atomic64_set(atomic64_t *v, long long i) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + + spin_lock_irqsave(lock, flags); + v->counter = i; + spin_unlock_irqrestore(lock, flags); +} + +void atomic64_add(long long a, atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + + spin_lock_irqsave(lock, flags); + v->counter += a; + spin_unlock_irqrestore(lock, flags); +} + +long long atomic64_add_return(long long a, atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter += a; + spin_unlock_irqrestore(lock, flags); + return val; +} + +void atomic64_sub(long long a, atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + + spin_lock_irqsave(lock, flags); + v->counter -= a; + spin_unlock_irqrestore(lock, flags); +} + +long long atomic64_sub_return(long long a, atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter -= a; + spin_unlock_irqrestore(lock, flags); + return val; +} + +long long atomic64_dec_if_positive(atomic64_t *v) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter - 1; + if (val >= 0) + v->counter = val; + spin_unlock_irqrestore(lock, flags); + return val; +} + +long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter; + if (val == o) + v->counter = n; + spin_unlock_irqrestore(lock, flags); + return val; +} + +long long atomic64_xchg(atomic64_t *v, long long new) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + long long val; + + spin_lock_irqsave(lock, flags); + val = v->counter; + v->counter = new; + spin_unlock_irqrestore(lock, flags); + return val; +} + +int atomic64_add_unless(atomic64_t *v, long long a, long long u) +{ + unsigned long flags; + spinlock_t *lock = lock_addr(v); + int ret = 1; + + spin_lock_irqsave(lock, flags); + if (v->counter != u) { + v->counter += a; + ret = 0; + } + spin_unlock_irqrestore(lock, flags); + return ret; +} + +static int init_atomic64_lock(void) +{ + int i; + + for (i = 0; i < NR_LOCKS; ++i) + spin_lock_init(&atomic64_lock[i].lock); + return 0; +} + +pure_initcall(init_atomic64_lock); |