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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_32.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_32.h')
-rw-r--r--arch/x86/include/asm/mutex_32.h125
1 files changed, 125 insertions, 0 deletions
diff --git a/arch/x86/include/asm/mutex_32.h b/arch/x86/include/asm/mutex_32.h
new file mode 100644
index 00000000000..25c16d8ba3c
--- /dev/null
+++ b/arch/x86/include/asm/mutex_32.h
@@ -0,0 +1,125 @@
+/*
+ * 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_32_H
+#define ASM_X86__MUTEX_32_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 /* ASM_X86__MUTEX_32_H */