[patch 03/11] mutex subsystem, add include/asm-i386/mutex.h

[Ingo Molnar]

add the i386 version of mutex.h, optimized in assembly.

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

----

 include/asm-i386/mutex.h |  102 +++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 102 insertions(+)

Index: linux/include/asm-i386/mutex.h
===================================================================
--- /dev/null
+++ linux/include/asm-i386/mutex.h
@@ -0,0 +1,102 @@
+/*
+ * Assembly implementation of the mutex fastpath, based on atomic
+ * decrement/increment.
+ *
+ * started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005 Red Hat, Inc., Ingo Molnar <mingo@xxxxxxxxxx>
+ */
+#ifndef _ASM_MUTEX_H
+#define _ASM_MUTEX_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, fn_name)				\
+do {									\
+	/* type-check the function too: */				\
+	void fastcall (*__tmp)(atomic_t *) = fn_name;			\
+	unsigned int dummy;						\
+									\
+	(void)__tmp;							\
+	typecheck(atomic_t *, count);					\
+									\
+	__asm__ __volatile__(						\
+		LOCK "decl (%%eax)\n"					\
+		"js 2f\n"						\
+		"1:\n"							\
+		LOCK_SECTION_START("")					\
+		"2: call "#fn_name"\n\t"				\
+		"jmp 1b\n"						\
+		LOCK_SECTION_END					\
+		:"=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
+ *  @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 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 (*fn_name)(atomic_t *))
+{
+	if (unlikely(atomic_dec_return(count) < 0))
+		return fn_name(count);
+	else
+		return 0;
+}
+
+/**
+ *  __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
+ *  @count: pointer of type atomic_t
+ *  @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 <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, fn_name)				\
+do {									\
+	/* type-check the function too: */				\
+	void fastcall (*__tmp)(atomic_t *) = fn_name;			\
+	unsigned int dummy;						\
+									\
+	(void)__tmp;							\
+	typecheck(atomic_t *, count);					\
+									\
+	__asm__ __volatile__(						\
+		LOCK "incl (%%eax)\n"					\
+		"jle 2f\n"						\
+		"1:\n"							\
+		LOCK_SECTION_START("")					\
+		"2: call "#fn_name"\n\t"				\
+		"jmp 1b\n"						\
+		LOCK_SECTION_END					\
+		:"=a" (dummy)						\
+		:"a" (count)						\
+		:"memory", "ecx", "edx");				\
+} while (0)
+
+#define __mutex_slowpath_needs_to_unlock()	1
+
+#endif
-
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