PowerPC fastpaths for mutex subsystem

[Joel Schopp]

This is the second pass at optimizing the fastpath for the new mutex subsystem 
on PowerPC.  I think it is ready to be included in the series with the other 
mutex patches now.  Tested on a 4 core (2 SMT threads/core) Power5 machine with 
gcc 3.3.2.

Test results from synchro-test.ko:

All tests run for default 5 seconds
Threads semaphores  mutexes     mutexes+attached
1       63,465,364  58,404,630  62,109,571
4       58,424,282  35,541,297  37,820,794
8       40,731,668  35,541,297  40,281,768
16      38,372,769  37,256,298  41,751,764
32      38,406,895  36,933,675  38,731,571
64      37,232,017  36,222,480  40,766,379

Signed-off-by: Joel Schopp <jschopp@xxxxxxxxxxxxxx>
Index: 2.6.15-mutex14/include/asm-powerpc/mutex.h
===================================================================
--- 2.6.15-mutex14.orig/include/asm-powerpc/mutex.h	2006-01-04 14:46:31.%N -0600
+++ 2.6.15-mutex14/include/asm-powerpc/mutex.h	2006-01-06 17:36:09.%N -0600
@@ -1,9 +1,84 @@
 /*
- * Pull in the generic implementation for the mutex fastpath.
+ * include/asm-powerpc/mutex.h
  *
- * TODO: implement optimized primitives instead, or leave the generic
- * implementation in place, or pick the atomic_xchg() based generic
- * implementation. (see asm-generic/mutex-xchg.h for details)
+ * PowerPC optimized mutex locking primitives
+ *
+ * Please look into asm-generic/mutex-xchg.h for a formal definition.
+ * Copyright (C) 2006 Joel Schopp <jschopp@xxxxxxxxxxxxxx>, IBM
  */
+#ifndef _ASM_MUTEX_H
+#define _ASM_MUTEX_H
+#define __mutex_fastpath_lock(count, fail_fn)\
+do{					\
+	int tmp;			\
+	__asm__ __volatile__(		\
+"1:	lwarx		%0,0,%1\n"	\
+"	addic		%0,%0,-1\n"	\
+"	stwcx.		%0,0,%1\n"	\
+"	bne-		1b\n"		\
+	ISYNC_ON_SMP			\
+	: "=&r" (tmp)			\
+	: "r" (&(count)->counter)	\
+	: "cr0", "memory");		\
+	if (unlikely(tmp < 0))		\
+		fail_fn(count);		\
+} while (0)
+
+#define __mutex_fastpath_unlock(count, fail_fn)\
+do{					\
+	int tmp;			\
+	__asm__ __volatile__(SYNC_ON_SMP\
+"1:	lwarx		%0,0,%1\n"	\
+"	addic		%0,%0,1\n"	\
+"	stwcx.		%0,0,%1\n"	\
+"	bne-		1b\n"		\
+	: "=&r" (tmp)			\
+	: "r" (&(count)->counter)	\
+	: "cr0", "memory");		\
+	if (unlikely(tmp <= 0))		\
+		fail_fn(count);		\
+} while (0)
+
+
+static inline int
+__mutex_fastpath_trylock(atomic_t* count, int (*fail_fn)(atomic_t*))
+{
+	int tmp;
+	__asm__ __volatile__(
+"1:	lwarx		%0,0,%1\n"
+"	cmpwi		0,%0,1\n"
+"	bne-		2f\n"
+"	addic		%0,%0,-1\n"
+"	stwcx.		%0,0,%1\n"
+"	bne-		1b\n"
+"	isync\n"
+"2:"
+	: "=&r" (tmp)
+	: "r" (&(count)->counter)
+	: "cr0", "memory");
+
+	return (int)tmp;
+
+}
+
+#define __mutex_slowpath_needs_to_unlock()		1
 
-#include <asm-generic/mutex-dec.h>
+static inline int
+__mutex_fastpath_lock_retval(atomic_t* count, int (*fail_fn)(atomic_t *))
+{
+	int tmp;
+	__asm__ __volatile__(
+"1:	lwarx		%0,0,%1\n"
+"	addic		%0,%0,-1\n"
+"	stwcx.		%0,0,%1\n"
+"	bne-		1b\n"
+"	isync		\n"
+	: "=&r" (tmp)
+	: "r" (&(count)->counter)
+	: "cr0", "memory");
+	if (unlikely(tmp < 0))
+		return fail_fn(count);
+	else
+		return 0;
+}
+#endif