cfq-iosched: don't schedule a dispatch for a non-idle queue

Vivek suggests we don't need schedule a dispatch when an idle queue
becomes nonidle. And he is right, cfq_should_preempt already covers
the logic.
Signed-off-by: NShaohua Li <shaohua.li@intel.com>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

block/cfq-iosched.c

@@ -3523,25 +3523,8 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
 		}
 	}
 
-	if (!cfqd->rq_in_driver) {
+	if (!cfqd->rq_in_driver)
 		cfq_schedule_dispatch(cfqd);
-		return;
-	}
-	/*
-	 * A queue is idle at cfq_dispatch_requests(), but it gets noidle
-	 * later. We schedule a dispatch if the queue has no requests,
-	 * otherwise the disk is actually in idle till all requests
-	 * are finished even cfq_arm_slice_timer doesn't make the queue idle
-	 * */
-	cfqq = cfqd->active_queue;
-	if (!cfqq)
-		return;
-
-	if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq) &&
-	    (!cfqd->cfq_group_idle || cfqq->cfqg->nr_cfqq > 1)) {
-		cfq_del_timer(cfqd, cfqq);
-		cfq_schedule_dispatch(cfqd);
-	}
 }
 
 /*