PERFORCE change 58472 for review
John Baldwin
jhb at FreeBSD.org
Thu Jul 29 11:08:07 PDT 2004
http://perforce.freebsd.org/chv.cgi?CH=58472
Change 58472 by jhb at jhb_slimer on 2004/07/29 18:07:13
Simplifiy the store_rel() optimization by just writing it in C
like the 80386 case. Also, adjust the comment above as far as
PentiumPro + vs. 80386.
Affected files ...
.. //depot/projects/smpng/sys/i386/include/atomic.h#14 edit
Differences ...
==== //depot/projects/smpng/sys/i386/include/atomic.h#14 (text+ko) ====
@@ -69,7 +69,7 @@
int atomic_cmpset_int(volatile u_int *dst, u_int exp, u_int src);
-#define ATOMIC_STORE_LOAD(TYPE, LOP, SOP) \
+#define ATOMIC_STORE_LOAD(TYPE, LOP) \
u_##TYPE atomic_load_acq_##TYPE(volatile u_##TYPE *p); \
void atomic_store_rel_##TYPE(volatile u_##TYPE *p, u_##TYPE v)
@@ -175,12 +175,12 @@
#if defined(I386_CPU)
/*
- * We assume that a = b will do atomic loads and stores.
- *
- * XXX: This is _NOT_ safe on a P6 or higher because it does not guarantee
- * memory ordering. These should only be used on a 386.
+ * We assume that a = b will do atomic loads and stores. However, on a
+ * PentiumPro or higher reads may pass writes, so for that case we have
+ * to use a serializing instruction (i.e. with LOCK) to do the load. For
+ * the 386 case, we can use a simple store since 386's don't support SMP.
*/
-#define ATOMIC_STORE_LOAD(TYPE, LOP, SOP, SCONS) \
+#define ATOMIC_STORE_LOAD(TYPE, LOP) \
static __inline u_##TYPE \
atomic_load_acq_##TYPE(volatile u_##TYPE *p) \
{ \
@@ -197,7 +197,7 @@
#else /* !defined(I386_CPU) */
-#define ATOMIC_STORE_LOAD(TYPE, LOP, SOP, SCONS) \
+#define ATOMIC_STORE_LOAD(TYPE, LOP) \
static __inline u_##TYPE \
atomic_load_acq_##TYPE(volatile u_##TYPE *p) \
{ \
@@ -214,10 +214,8 @@
static __inline void \
atomic_store_rel_##TYPE(volatile u_##TYPE *p, u_##TYPE v)\
{ \
- __asm __volatile(SOP \
- : "=m" (*p), /* 0 */ \
- : SCONS (v) /* 1 */ \
- : "memory"); \
+ *p = v; \
+ __asm __volatile("" : : : "memory"); \
} \
struct __hack
@@ -227,7 +225,7 @@
extern int atomic_cmpset_int(volatile u_int *, u_int, u_int);
-#define ATOMIC_STORE_LOAD(TYPE, LOP, SOP, SCONS) \
+#define ATOMIC_STORE_LOAD(TYPE, LOP) \
extern u_##TYPE atomic_load_acq_##TYPE(volatile u_##TYPE *p); \
extern void atomic_store_rel_##TYPE(volatile u_##TYPE *p, u_##TYPE v)
@@ -255,10 +253,10 @@
ATOMIC_ASM(add, long, "addl %1,%0", "ir", v);
ATOMIC_ASM(subtract, long, "subl %1,%0", "ir", v);
-ATOMIC_STORE_LOAD(char, "cmpxchgb %b0,%1", "movb %b1,%0", "iq");
-ATOMIC_STORE_LOAD(short,"cmpxchgw %w0,%1", "movw %w1,%0", "ir");
-ATOMIC_STORE_LOAD(int, "cmpxchgl %0,%1", "movl %1,%0", "ir");
-ATOMIC_STORE_LOAD(long, "cmpxchgl %0,%1", "movl %1,%0", "ir");
+ATOMIC_STORE_LOAD(char, "cmpxchgb %b0,%1");
+ATOMIC_STORE_LOAD(short,"cmpxchgw %w0,%1");
+ATOMIC_STORE_LOAD(int, "cmpxchgl %0,%1");
+ATOMIC_STORE_LOAD(long, "cmpxchgl %0,%1");
#undef ATOMIC_ASM
#undef ATOMIC_STORE_LOAD
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