[dm-devel] [PATCH] dm: pass up rotational flag

[Mandeep Singh Baines]

Allow the NONROT flag to be passed through to linear mappings if all
underlying device are non-rotational. Tools like ureadahead will
schedule IOs differently based on the rotational flag.

With this patch, I see boot time go from 7.75 s to 7.46 s on my device.

Suggested-by: J. Richard Barnette <jrbarnette at chromium.org>
Signed-off-by: Mandeep Singh Baines <msb at chromium.org>
Cc: Neil Brown <neilb at suse.de>
Cc: Mike Snitzer <snitzer at redhat.com>
Cc: Jens Axboe <jaxboe at fusionio.com>
Cc: Martin K. Petersen <martin.petersen at oracle.com>
Cc: Alasdair G Kergon <agk at redhat.com>
Cc: dm-devel at redhat.com
---
 drivers/md/dm-table.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index cb8380c..40c6071 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1177,6 +1177,30 @@ static void dm_table_set_integrity(struct dm_table *t)
 			       blk_get_integrity(template_disk));
 }
 
+static int device_nonrot(struct dm_target *ti, struct dm_dev *dev,
+			       sector_t start, sector_t len, void *data)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+
+	return q && blk_queue_nonrot(q);
+}
+
+static bool dm_table_all_nonrot(struct dm_table *t)
+{
+	unsigned i = 0;
+
+	/* Ensure that all underlying device are non rotational. */
+	while (i < dm_table_get_num_targets(t)) {
+		struct dm_target *ti = dm_table_get_target(t, i++);
+
+		if (!ti->type->iterate_devices ||
+		    !ti->type->iterate_devices(ti, device_nonrot, NULL))
+			return false;
+	}
+
+	return true;
+}
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 			       struct queue_limits *limits)
 {
@@ -1189,6 +1213,10 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, q);
 	else
 		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
+	if (!dm_table_all_nonrot(t))
+		queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
+	else
+		queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
 
 	dm_table_set_integrity(t);
 
-- 
1.7.3.1