[PATCH] mutex subsystem, add include/asm-x86_64/mutex.h

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>

1 files changed, 113 insertions, 0 deletions

diff --git a/include/asm-x86_64/mutex.h b/include/asm-x86_64/mutex.h
new file mode 100644
index 000000000000..818abfd262d1
--- /dev/null
+++ b/include/asm-x86_64/mutex.h
@@ -0,0 +1,113 @@
+/*
+ * 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 - 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(fastcall void (*)(atomic_t *), fail_fn);           \
+                                                                        \
+        __asm__ __volatile__(                                           \
+                LOCK    "   decl (%%rdi)        \n"                     \
+                        "   js 2f               \n"                     \
+                        "1:                     \n"                     \
+                                                                        \
+                LOCK_SECTION_START("")                                  \
+                        "2: call "#fail_fn"     \n"                     \
+                        "   jmp 1b              \n"                     \
+                LOCK_SECTION_END                                        \
+                                                                        \
+                :"=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 fastcall (*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(fastcall void (*)(atomic_t *), fail_fn);           \
+                                                                        \
+        __asm__ __volatile__(                                           \
+                LOCK    "   incl (%%rdi)        \n"                     \
+                        "   jle 2f              \n"                     \
+                        "1:                     \n"                     \
+                                                                        \
+                LOCK_SECTION_START("")                                  \
+                        "2: call "#fail_fn"     \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
+ *  @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