deepin: only use BFQ as the elevator for single queue rotate devices

Why: bfq elevator shows high bandwidth in read/write than other in hdd.[1]

Question:
It is correct time to get the flag?

If we can get the flag,so we can only use BFQ elevator for hdd.
or it is same as before.

Answer:
It is ok for:
use this macro:blk_queue_flag_set(QUEUE_FLAG_NONROT
for no rotate block device like ssd:
blk_queue_flag_set(QUEUE_FLAG_NONROT
device_add_disk->
elevator_init_mq->
elevator_get_default-> choose mq-deadline
for rotate device like hdd:
device_add_disk->
elevator_init_mq->
elevator_get_default-> choose bfq

Link:https://ieeexplore.ieee.org/document/7469567 [1]

Signed-off-by: Wentao Guan <[email protected]>

block/elevator.c

@@ -576,7 +576,9 @@ static struct elevator_type *elevator_get_default(struct request_queue *q)
 	    !blk_mq_is_shared_tags(q->tag_set->flags))
 		return NULL;
 #if defined(CONFIG_IOSCHED_BFQ)
-	return elevator_find_get(q, "bfq");
+	if (!blk_queue_nonrot(q))
+		return elevator_find_get(q, "bfq");
+	return elevator_find_get(q, "mq-deadline");
 #else
 	return elevator_find_get(q, "mq-deadline");
 #endif