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110 lines
3.3 KiB
110 lines
3.3 KiB
/* |
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* Assembly implementation of the mutex fastpath, based on atomic |
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* decrement/increment. |
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* |
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* started by Ingo Molnar: |
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* |
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
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*/ |
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#ifndef _ASM_X86_MUTEX_32_H |
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#define _ASM_X86_MUTEX_32_H |
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#include <asm/alternative.h> |
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/** |
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* __mutex_fastpath_lock - try to take the lock by moving the count |
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* from 1 to a 0 value |
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* @count: pointer of type atomic_t |
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* @fn: function to call if the original value was not 1 |
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* |
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* Change the count from 1 to a value lower than 1, and call <fn> if it |
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* wasn't 1 originally. This function MUST leave the value lower than 1 |
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* even when the "1" assertion wasn't true. |
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*/ |
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#define __mutex_fastpath_lock(count, fail_fn) \ |
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do { \ |
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unsigned int dummy; \ |
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\ |
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typecheck(atomic_t *, count); \ |
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typecheck_fn(void (*)(atomic_t *), fail_fn); \ |
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\ |
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asm volatile(LOCK_PREFIX " decl (%%eax)\n" \ |
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" jns 1f \n" \ |
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" call " #fail_fn "\n" \ |
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"1:\n" \ |
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: "=a" (dummy) \ |
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: "a" (count) \ |
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: "memory", "ecx", "edx"); \ |
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} while (0) |
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/** |
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* __mutex_fastpath_lock_retval - try to take the lock by moving the count |
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* from 1 to a 0 value |
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* @count: pointer of type atomic_t |
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* |
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* Change the count from 1 to a value lower than 1. This function returns 0 |
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* if the fastpath succeeds, or -1 otherwise. |
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*/ |
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static inline int __mutex_fastpath_lock_retval(atomic_t *count) |
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{ |
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if (unlikely(atomic_dec_return(count) < 0)) |
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return -1; |
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else |
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return 0; |
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} |
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/** |
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* __mutex_fastpath_unlock - try to promote the mutex from 0 to 1 |
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* @count: pointer of type atomic_t |
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* @fail_fn: function to call if the original value was not 0 |
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* |
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* try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>. |
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* In the failure case, this function is allowed to either set the value |
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* to 1, or to set it to a value lower than 1. |
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* |
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* If the implementation sets it to a value of lower than 1, the |
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* __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs |
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* to return 0 otherwise. |
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*/ |
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#define __mutex_fastpath_unlock(count, fail_fn) \ |
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do { \ |
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unsigned int dummy; \ |
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\ |
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typecheck(atomic_t *, count); \ |
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typecheck_fn(void (*)(atomic_t *), fail_fn); \ |
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\ |
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asm volatile(LOCK_PREFIX " incl (%%eax)\n" \ |
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" jg 1f\n" \ |
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" call " #fail_fn "\n" \ |
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"1:\n" \ |
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: "=a" (dummy) \ |
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: "a" (count) \ |
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: "memory", "ecx", "edx"); \ |
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} while (0) |
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#define __mutex_slowpath_needs_to_unlock() 1 |
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/** |
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* __mutex_fastpath_trylock - try to acquire the mutex, without waiting |
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* |
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* @count: pointer of type atomic_t |
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* @fail_fn: fallback function |
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* |
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* Change the count from 1 to a value lower than 1, and return 0 (failure) |
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* if it wasn't 1 originally, or return 1 (success) otherwise. This function |
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* MUST leave the value lower than 1 even when the "1" assertion wasn't true. |
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* Additionally, if the value was < 0 originally, this function must not leave |
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* it to 0 on failure. |
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*/ |
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static inline int __mutex_fastpath_trylock(atomic_t *count, |
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int (*fail_fn)(atomic_t *)) |
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{ |
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/* cmpxchg because it never induces a false contention state. */ |
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if (likely(atomic_cmpxchg(count, 1, 0) == 1)) |
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return 1; |
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return 0; |
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} |
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#endif /* _ASM_X86_MUTEX_32_H */
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