[PATCH] aio: reorder kiocb structure elements to make sync iocb setup faster

Reorder members of the kiocb structure to make sync kiocb setup faster.  By
setting the elements sequentially, the write combining buffers on the CPU
are able to combine the writes into a single burst, which results in fewer
cache cycles being consumed, freeing them up for other code.  This results
in a 10-20KB/s[*] increase on the bw_unix part of LMbench on my test
system.

* The improvement varies based on what other patches are in the system,
  as there are a number of bottlenecks, so this number is not absolutely
  accurate.

Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/aio.h

@@ -94,26 +94,27 @@ struct kiocb {
 	ssize_t			(*ki_retry)(struct kiocb *);
 	void			(*ki_dtor)(struct kiocb *);
 
-	struct list_head	ki_list;	/* the aio core uses this
-						 * for cancellation */
-
 	union {
 		void __user		*user;
 		struct task_struct	*tsk;
 	} ki_obj;
+
 	__u64			ki_user_data;	/* user's data for completion */
+	wait_queue_t		ki_wait;
 	loff_t			ki_pos;
+
+	void			*private;
 	/* State that we remember to be able to restart/retry  */
 	unsigned short		ki_opcode;
 	size_t			ki_nbytes; 	/* copy of iocb->aio_nbytes */
 	char 			__user *ki_buf;	/* remaining iocb->aio_buf */
 	size_t			ki_left; 	/* remaining bytes */
-	wait_queue_t		ki_wait;
 	long			ki_retried; 	/* just for testing */
 	long			ki_kicked; 	/* just for testing */
 	long			ki_queued; 	/* just for testing */
 
-	void			*private;
+	struct list_head	ki_list;	/* the aio core uses this
+						 * for cancellation */
 };
 
 #define is_sync_kiocb(iocb)	((iocb)->ki_key == KIOCB_SYNC_KEY)
@@ -126,6 +127,7 @@ struct kiocb {
 		(x)->ki_filp = (filp);			\
 		(x)->ki_ctx = NULL;			\
 		(x)->ki_cancel = NULL;			\
+		(x)->ki_retry = NULL;			\
 		(x)->ki_dtor = NULL;			\
 		(x)->ki_obj.tsk = tsk;			\
 		(x)->ki_user_data = 0;                  \