Use lwsync to provide memory barriers on systems that support it instead

of sync (lwsync is an alternate encoding of sync on systems that do not
support it, providing graceful fallback). This provides more than an order
of magnitude reduction in the time required to acquire or release a mutex.

MFC after:	2 months

1 files changed, 18 insertions, 20 deletions

diff --git a/sys/powerpc/include/atomic.h b/sys/powerpc/include/atomic.h
index 77f5732..9a77dc2 100644
--- a/sys/powerpc/include/atomic.h
+++ b/sys/powerpc/include/atomic.h
@@ -36,12 +36,10 @@
 #error this file needs sys/cdefs.h as a prerequisite
 #endif
 
-#define	__ATOMIC_BARRIER					\
-    __asm __volatile("sync" : : : "memory")
-
-#define mb()	__ATOMIC_BARRIER
-#define	wmb()	mb()
-#define	rmb()	mb()
+/* NOTE: lwsync is equivalent to sync on systems without lwsync */
+#define mb()	__asm __volatile("lwsync" : : : "memory")
+#define wmb()	__asm __volatile("lwsync" : : : "memory")
+#define rmb()	__asm __volatile("lwsync" : : : "memory")
 
 /*
  * atomic_add(p, v)
@@ -94,13 +92,13 @@
     atomic_add_acq_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
 	__atomic_add_##type(p, v, t);				\
-	__ATOMIC_BARRIER;					\
+	rmb();							\
     }								\
 								\
     static __inline void					\
     atomic_add_rel_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
-	__ATOMIC_BARRIER;					\
+	wmb();							\
 	__atomic_add_##type(p, v, t);				\
     }								\
     /* _ATOMIC_ADD */
@@ -180,13 +178,13 @@ _ATOMIC_ADD(long)
     atomic_clear_acq_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
 	__atomic_clear_##type(p, v, t);				\
-	__ATOMIC_BARRIER;					\
+	rmb();							\
     }								\
 								\
     static __inline void					\
     atomic_clear_rel_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
-	__ATOMIC_BARRIER;					\
+	wmb();							\
 	__atomic_clear_##type(p, v, t);				\
     }								\
     /* _ATOMIC_CLEAR */
@@ -282,13 +280,13 @@ _ATOMIC_CLEAR(long)
     atomic_set_acq_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
 	__atomic_set_##type(p, v, t);				\
-	__ATOMIC_BARRIER;					\
+	rmb();							\
     }								\
 								\
     static __inline void					\
     atomic_set_rel_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;						\
-	__ATOMIC_BARRIER;					\
+	wmb();							\
 	__atomic_set_##type(p, v, t);				\
     }								\
     /* _ATOMIC_SET */
@@ -368,13 +366,13 @@ _ATOMIC_SET(long)
     atomic_subtract_acq_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;							\
 	__atomic_subtract_##type(p, v, t);				\
-	__ATOMIC_BARRIER;						\
+	rmb();								\
     }									\
 									\
     static __inline void						\
     atomic_subtract_rel_##type(volatile u_##type *p, u_##type v) {	\
 	u_##type t;							\
-	__ATOMIC_BARRIER;						\
+	wmb();								\
 	__atomic_subtract_##type(p, v, t);				\
     }									\
     /* _ATOMIC_SUBTRACT */
@@ -481,14 +479,14 @@ atomic_load_acq_##TYPE(volatile u_##TYPE *p)			\
 	u_##TYPE v;						\
 								\
 	v = *p;							\
-	__ATOMIC_BARRIER;					\
+	rmb();							\
 	return (v);						\
 }								\
 								\
 static __inline void						\
 atomic_store_rel_##TYPE(volatile u_##TYPE *p, u_##TYPE v)	\
 {								\
-	__ATOMIC_BARRIER;					\
+	wmb();							\
 	*p = v;							\
 }
 
@@ -598,14 +596,14 @@ atomic_cmpset_acq_int(volatile u_int *p, u_int cmpval, u_int newval)
 	int retval;
 
 	retval = atomic_cmpset_int(p, cmpval, newval);
-	__ATOMIC_BARRIER;
+	rmb();
 	return (retval);
 }
 
 static __inline int
 atomic_cmpset_rel_int(volatile u_int *p, u_int cmpval, u_int newval)
 {
-	__ATOMIC_BARRIER;
+	wmb();
 	return (atomic_cmpset_int(p, cmpval, newval));
 }
 
@@ -615,14 +613,14 @@ atomic_cmpset_acq_long(volatile u_long *p, u_long cmpval, u_long newval)
 	u_long retval;
 
 	retval = atomic_cmpset_long(p, cmpval, newval);
-	__ATOMIC_BARRIER;
+	rmb();
 	return (retval);
 }
 
 static __inline int
 atomic_cmpset_rel_long(volatile u_long *p, u_long cmpval, u_long newval)
 {
-	__ATOMIC_BARRIER;
+	wmb();
 	return (atomic_cmpset_long(p, cmpval, newval));
 }