[PATCH 6/9] block/mq-deadline: Reduce the read expiry time for non-rotational media

[Bart Van Assche <bvanassche@acm.org>]

Rotational media (hard disks) benefit more from merging requests than
non-rotational media. Reduce the read expire time for non-rotational media
to reduce read latency.

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/mq-deadline.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index dfbc6b77fa71..2ab844a4b6b5 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -29,7 +29,9 @@
 /*
  * See Documentation/block/deadline-iosched.rst
  */
-static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
+/* max time before a read is submitted. */
+static const int read_expire_rot = HZ / 2;
+static const int read_expire_nonrot = 1;
 static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
 static const int writes_starved = 2;    /* max times reads can starve a write */
 static const int fifo_batch = 16;       /* # of sequential requests treated as one
@@ -430,7 +432,8 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
 	INIT_LIST_HEAD(&dd->fifo_list[DD_WRITE]);
 	dd->sort_list[DD_READ] = RB_ROOT;
 	dd->sort_list[DD_WRITE] = RB_ROOT;
-	dd->fifo_expire[DD_READ] = read_expire;
+	dd->fifo_expire[DD_READ] = blk_queue_nonrot(q) ? read_expire_nonrot :
+		read_expire_rot;
 	dd->fifo_expire[DD_WRITE] = write_expire;
 	dd->writes_starved = writes_starved;
 	dd->front_merges = 1;