[PATCH] cfq-iosched: correctly set ioprio on both targets

Patch originally from Vasily Tarasov <vtaras@sw.ru>

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.
Signed-off-by: Jens Axboe <axboe@suse.de>

block/cfq-iosched.c

@@ -1388,10 +1388,9 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
 			}
 		}
 		cfqq = cic->cfqq[SYNC];
-		if (cfqq) {
+		if (cfqq)
 			cfq_mark_cfqq_prio_changed(cfqq);
-			cfq_init_prio_data(cfqq);
-		}
+
 		spin_unlock(cfqd->queue->queue_lock);
 	}
 }