list: remove prefetching from regular list iterators

This is removes the use of software prefetching from the regular list
iterators.  We don't want it.  If you do want to prefetch in some
iterator of yours, go right ahead.  Just don't expect the iterator to do
it, since normally the downsides are bigger than the upsides.

It also replaces <linux/prefetch.h> with <linux/const.h>, because the
use of LIST_POISON ends up needing it.  <linux/poison.h> is sadly not
self-contained, and including prefetch.h just happened to hide that.

Suggested by David Miller (networking has a lot of regular lists that
are often empty or a single entry, and prefetching is not going to do
anything but add useless instructions).

Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: linux-arch@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 900a97a..e3beb31 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -253,7 +253,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
  */
 #define list_for_each_entry_rcu(pos, head, member) \
 	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
-		prefetch(pos->member.next), &pos->member != (head); \
+		&pos->member != (head); \
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 
@@ -270,7 +270,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
  */
 #define list_for_each_continue_rcu(pos, head) \
 	for ((pos) = rcu_dereference_raw(list_next_rcu(pos)); \
-		prefetch((pos)->next), (pos) != (head); \
+		(pos) != (head); \
 		(pos) = rcu_dereference_raw(list_next_rcu(pos)))
 
 /**
@@ -284,7 +284,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
  */
 #define list_for_each_entry_continue_rcu(pos, head, member) 		\
 	for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
-	     prefetch(pos->member.next), &pos->member != (head);	\
+	     &pos->member != (head);	\
 	     pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**