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Diffstat (limited to 'arch/x86/include/asm/mutex_32.h')
| -rw-r--r-- | arch/x86/include/asm/mutex_32.h | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/arch/x86/include/asm/mutex_32.h b/arch/x86/include/asm/mutex_32.h new file mode 100644 index 000000000000..25c16d8ba3c7 --- /dev/null +++ b/arch/x86/include/asm/mutex_32.h @@ -0,0 +1,125 @@ +/* + * Assembly implementation of the mutex fastpath, based on atomic + * decrement/increment. + * + * started by Ingo Molnar: + * + * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> + */ +#ifndef ASM_X86__MUTEX_32_H +#define ASM_X86__MUTEX_32_H + +#include <asm/alternative.h> + +/** + * __mutex_fastpath_lock - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fn> if it + * wasn't 1 originally. This function MUST leave the value lower than 1 + * even when the "1" assertion wasn't true. + */ +#define __mutex_fastpath_lock(count, fail_fn) \ +do { \ + unsigned int dummy; \ + \ + typecheck(atomic_t *, count); \ + typecheck_fn(void (*)(atomic_t *), fail_fn); \ + \ + asm volatile(LOCK_PREFIX " decl (%%eax)\n" \ + " jns 1f \n" \ + " call " #fail_fn "\n" \ + "1:\n" \ + : "=a" (dummy) \ + : "a" (count) \ + : "memory", "ecx", "edx"); \ +} while (0) + + +/** + * __mutex_fastpath_lock_retval - try to take the lock by moving the count + * from 1 to a 0 value + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 1 + * + * Change the count from 1 to a value lower than 1, and call <fail_fn> if it + * wasn't 1 originally. This function returns 0 if the fastpath succeeds, + * or anything the slow path function returns + */ +static inline int __mutex_fastpath_lock_retval(atomic_t *count, + int (*fail_fn)(atomic_t *)) +{ + if (unlikely(atomic_dec_return(count) < 0)) + return fail_fn(count); + else + return 0; +} + +/** + * __mutex_fastpath_unlock - try to promote the mutex from 0 to 1 + * @count: pointer of type atomic_t + * @fail_fn: function to call if the original value was not 0 + * + * try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>. + * In the failure case, this function is allowed to either set the value + * to 1, or to set it to a value lower than 1. + * + * If the implementation sets it to a value of lower than 1, the + * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs + * to return 0 otherwise. + */ +#define __mutex_fastpath_unlock(count, fail_fn) \ +do { \ + unsigned int dummy; \ + \ + typecheck(atomic_t *, count); \ + typecheck_fn(void (*)(atomic_t *), fail_fn); \ + \ + asm volatile(LOCK_PREFIX " incl (%%eax)\n" \ + " jg 1f\n" \ + " call " #fail_fn "\n" \ + "1:\n" \ + : "=a" (dummy) \ + : "a" (count) \ + : "memory", "ecx", "edx"); \ +} while (0) + +#define __mutex_slowpath_needs_to_unlock() 1 + +/** + * __mutex_fastpath_trylock - try to acquire the mutex, without waiting + * + * @count: pointer of type atomic_t + * @fail_fn: fallback function + * + * Change the count from 1 to a value lower than 1, and return 0 (failure) + * if it wasn't 1 originally, or return 1 (success) otherwise. This function + * MUST leave the value lower than 1 even when the "1" assertion wasn't true. + * Additionally, if the value was < 0 originally, this function must not leave + * it to 0 on failure. + */ +static inline int __mutex_fastpath_trylock(atomic_t *count, + int (*fail_fn)(atomic_t *)) +{ + /* + * We have two variants here. The cmpxchg based one is the best one + * because it never induce a false contention state. It is included + * here because architectures using the inc/dec algorithms over the + * xchg ones are much more likely to support cmpxchg natively. + * + * If not we fall back to the spinlock based variant - that is + * just as efficient (and simpler) as a 'destructive' probing of + * the mutex state would be. + */ +#ifdef __HAVE_ARCH_CMPXCHG + if (likely(atomic_cmpxchg(count, 1, 0) == 1)) + return 1; + return 0; +#else + return fail_fn(count); +#endif +} + +#endif /* ASM_X86__MUTEX_32_H */ |