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authorAl Viro <viro@zeniv.linux.org.uk>2008-08-17 21:05:42 -0400
committerH. Peter Anvin <hpa@zytor.com>2008-10-22 22:55:20 -0700
commitbb8985586b7a906e116db835c64773b7a7d51663 (patch)
treede93ae58e88cc563d95cc124a73f3930594c6100 /arch/x86/include/asm/mutex_64.h
parent8ede0bdb63305d3353efd97e9af6210afb05734e (diff)
x86, um: ... and asm-x86 move
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/include/asm/mutex_64.h')
-rw-r--r--arch/x86/include/asm/mutex_64.h100
1 files changed, 100 insertions, 0 deletions
diff --git a/arch/x86/include/asm/mutex_64.h b/arch/x86/include/asm/mutex_64.h
new file mode 100644
index 000000000000..918ba21ab9d9
--- /dev/null
+++ b/arch/x86/include/asm/mutex_64.h
@@ -0,0 +1,100 @@
+/*
+ * 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_X86__MUTEX_64_H
+#define ASM_X86__MUTEX_64_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(void (*)(atomic_t *), fail_fn); \
+ \
+ asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
+ " jns 1f \n" \
+ " call " #fail_fn "\n" \
+ "1:" \
+ : "=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 (*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(void (*)(atomic_t *), fail_fn); \
+ \
+ asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
+ " jg 1f\n" \
+ " call " #fail_fn "\n" \
+ "1:" \
+ : "=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 /* ASM_X86__MUTEX_64_H */