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Commit b8aa0361 authored by Ingo Molnar's avatar Ingo Molnar Committed by Ingo Molnar
Browse files

[PATCH] mutex subsystem, add include/asm-x86_64/mutex.h 



add the x86_64 version of mutex.h, optimized in assembly.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarArjan van de Ven <arjan@infradead.org>
parent 2af7f59e

include/asm-x86_64/mutex.h

0 → 100644
+113 −0
Original line number Diff line number Diff line 
/*

 * 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



/**

 * __mutex_fastpath_lock - decrement and call function if negative

 * @v: pointer of type atomic_t

 * @fail_fn: function to call if the result is negative

 *

 * Atomically decrements @v and calls <fail_fn> if the result is negative.

 */

#define __mutex_fastpath_lock(v, fail_fn)				\

do {									\

	unsigned long dummy;						\

									\

	typecheck(atomic_t *, v);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ __volatile__(						\

		LOCK	"   decl (%%rdi)	\n"			\

			"   js 2f		\n"			\

			"1:			\n"			\

									\

		LOCK_SECTION_START("")					\

			"2: call "#fail_fn"	\n"			\

			"   jmp 1b		\n"			\

		LOCK_SECTION_END					\

									\

		:"=D" (dummy)						\

		: "D" (v)						\

		: "rax", "rsi", "rdx", "rcx",				\

		  "r8", "r9", "r10", "r11", "memory");			\

} 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 fastcall (*fail_fn)(atomic_t *))

{

	if (unlikely(atomic_dec_return(count) < 0))

		return fail_fn(count);

	else

		return 0;

}



/**

 * __mutex_fastpath_unlock - increment and call function if nonpositive

 * @v: pointer of type atomic_t

 * @fail_fn: function to call if the result is nonpositive

 *

 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.

 */

#define __mutex_fastpath_unlock(v, fail_fn)				\

do {									\

	unsigned long dummy;						\

									\

	typecheck(atomic_t *, v);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ __volatile__(						\

		LOCK	"   incl (%%rdi)	\n"			\

			"   jle 2f		\n"			\

			"1:			\n"			\

									\

		LOCK_SECTION_START("")					\

			"2: call "#fail_fn"	\n"			\

			"   jmp 1b		\n"			\

		LOCK_SECTION_END					\

									\

		:"=D" (dummy)						\

		: "D" (v)						\

		: "rax", "rsi", "rdx", "rcx",				\

		  "r8", "r9", "r10", "r11", "memory");			\

} 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 0 and return 1 (success), or return 0 (failure)

 * if it wasn't 1 originally. [the fallback function is never used on

 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]

 */

static inline int

__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))

{

	if (likely(atomic_cmpxchg(count, 1, 0)) == 1)

		return 1;

	else

		return 0;

}



#endif