[patch 04/13] mutex subsystem, add include/asm-x86_64/mutex.h

[patch 04/13] mutex subsystem, add include/asm-x86_64/mutex.h

[Ingo Molnar]

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

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>

----

 include/asm-x86_64/mutex.h |   97 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 97 insertions(+)

Index: linux/include/asm-x86_64/mutex.h
===================================================================
--- /dev/null
+++ linux/include/asm-x86_64/mutex.h
@@ -0,0 +1,97 @@
+/*
+ * 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@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
+ * @fn: function to call if the result is negative
+ *
+ * Atomically decrements @v and calls <fn> if the result is negative.
+ */
+#define __mutex_fastpath_lock(v, fn_name)				\
+do {									\
+	/* type-check the function too: */				\
+	fastcall void (*__tmp)(atomic_t *) = fn_name;			\
+	unsigned long dummy;						\
+									\
+	(void)__tmp;							\
+	typecheck(atomic_t *, v);					\
+									\
+	__asm__ __volatile__(						\
+		LOCK	"   decl (%%rdi)	\n"			\
+			"   js 2f		\n"			\
+			"1:			\n"			\
+									\
+		LOCK_SECTION_START("")					\
+			"2: call "#fn_name"	\n"			\
+			"   jmp 1b		\n"			\
+		LOCK_SECTION_END					\
+									\
+		:"=D" (dummy)						\
+		: "D" (v)						\
+		: "rax", "rsi", "rdx", "rcx",				\
+		  "r8", "r9", "r10", "r11", "memory");			\
+} while (0)
+
+/**
+ * __mutex_fastpath_unlock - increment and call function if nonpositive
+ * @v: pointer of type atomic_t
+ * @fn: function to call if the result is nonpositive
+ *
+ * Atomically increments @v and calls <fn> if the result is nonpositive.
+ */
+#define __mutex_fastpath_unlock(v, fn_name)				\
+do {									\
+	/* type-check the function too: */				\
+	fastcall void (*__tmp)(atomic_t *) = fn_name;			\
+	unsigned long dummy;						\
+									\
+	(void)__tmp;							\
+	typecheck(atomic_t *, v);					\
+									\
+	__asm__ __volatile__(						\
+		LOCK	"   incl (%%rdi)	\n"			\
+			"   jle 2f		\n"			\
+			"1:			\n"			\
+									\
+		LOCK_SECTION_START("")					\
+			"2: call "#fn_name"	\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
+ *  @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 (*fn)(atomic_t *))
+{
+	if (likely(atomic_cmpxchg(count, 1, 0)) == 1)
+		return 1;
+	else
+		return 0;
+}
+
+#endif