[PATCH] mutex subsystem, add include/asm-i386/mutex.h

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

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

1 files changed, 124 insertions, 0 deletions

diff --git a/include/asm-i386/mutex.h b/include/asm-i386/mutex.h
new file mode 100644
index 000000000000..4e5e3de1b9a6
--- /dev/null
+++ b/include/asm-i386/mutex.h
@@ -0,0 +1,124 @@
+/*
+ * 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 - 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(fastcall void (*)(atomic_t *), fail_fn);           \
+                                                                        \
+        __asm__ __volatile__(                                           \
+                LOCK    "   decl (%%eax)        \n"                     \
+                        "   js "#fail_fn"       \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 fastcall (*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(fastcall void (*)(atomic_t *), fail_fn);           \
+                                                                        \
+        __asm__ __volatile__(                                           \
+                LOCK    "   incl (%%eax)        \n"                     \
+                        "   jle "#fail_fn"      \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