CFQ ioprio setting patch

[Vasily Tarasov]

If you set io-priority of process 1 using sys_ioprio_set system call by 
another process 2 (like ionice do),
then cfq_init_prio_data() function sets priority of process 2 (current) 
on queue of process 1 and clears the flag, that designates change of ioprio.
So the process  1 will work like with priority of process 2.

I propose not to call cfq_init_prio_data() on io-priority change, but 
only mark queue as queue with changed prority.
Every time when new request comes cfq-scheduler checks for this flag and 
atomaticaly changes priority of queue to new value.

Small patch is below.
--- linux-2.6.16-026stab012-ioprio/block/cfq-iosched.c.orig	2006-05-29 13:46:20.000000000 +0400
+++ linux-2.6.16-026stab012-ioprio/block/cfq-iosched.c	2006-05-24 15:31:24.000000000 +0400
@@ -1325,7 +1325,6 @@ static inline void changed_ioprio(struct
 
 		spin_lock(cfqd->queue->queue_lock);
 		cfq_mark_cfqq_prio_changed(cfqq);
-		cfq_init_prio_data(cfqq);
 		spin_unlock(cfqd->queue->queue_lock);
 	}
 }