130 строки
3.9 KiB
C
130 строки
3.9 KiB
C
/*
|
|
* 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_MUTEX_H
|
|
#define _ASM_MUTEX_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
|