Linus, please apply. atomic ops are *not* barriers any more.
Sebastian Wilhelmi <wilhelmi@ira.uka.de>: Re: Question on your "Unreliable Guide To Locking":
> Yes, this is no longer true. The modern assumptions are that they are
> not barriers.
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.6-pre3/Documentation/DocBook/kernel-locking.tmpl trivial-2.5.6-pre3/Documentation/DocBook/kernel-locking.tmpl
--- linux-2.5.6-pre3/Documentation/DocBook/kernel-locking.tmpl Sun May 20 10:43:05 2001
+++ trivial-2.5.6-pre3/Documentation/DocBook/kernel-locking.tmpl Thu Mar 7 18:20:33 2002
@@ -788,8 +788,18 @@
</para>
<para>
- Note that the atomic operations are defined to act as both
- read and write barriers on all platforms.
+ Note that the atomic operations do in general not act as memory
+ barriers. Instead you can insert a memory barrier before or
+ after <function>atomic_inc()</function> or
+ <function>atomic_dec()</function> by inserting
+ <function>smp_mb__before_atomic_inc()</function>,
+ <function>smp_mb__after_atomic_inc()</function>,
+ <function>smp_mb__before_atomic_dec()</function> or
+ <function>smp_mb__after_atomic_dec()</function>
+ respectively. The advantage of using those macros instead of
+ <function>smp_mb()</function> is, that they are cheaper on some
+ platforms.
+ <!-- Sebastian Wilhelmi <seppi@seppi.de> 2002-03-04 -->
</para>
</sect1>
-- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Mar 07 2002 - 21:01:00 EST