dm table: propagate non rotational flag

Allow QUEUE_FLAG_NONROT to propagate up the device stack if all
underlying devices 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@chromium.org>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Jens Axboe <jaxboe@fusionio.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: dm-devel@redhat.com
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index bc04518e9d8..81cbbf375bd 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1299,6 +1299,31 @@ static bool dm_table_discard_zeroes_data(struct dm_table *t)
         return 1;
 }
 
+static int device_is_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_is_nonrot(struct dm_table *t)
+{
+        struct dm_target *ti;
+        unsigned i = 0;
+
+        /* Ensure that all underlying device are non-rotational. */
+        while (i < dm_table_get_num_targets(t)) {
+                ti = dm_table_get_target(t, i++);
+
+                if (!ti->type->iterate_devices ||
+                    !ti->type->iterate_devices(ti, device_is_nonrot, NULL))
+                        return 0;
+        }
+
+        return 1;
+}
+
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
                                struct queue_limits *limits)
 {
@@ -1324,6 +1349,11 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
         if (!dm_table_discard_zeroes_data(t))
                 q->limits.discard_zeroes_data = 0;
 
+        if (dm_table_is_nonrot(t))
+                queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
+        else
+                queue_flag_clear_unlocked(QUEUE_FLAG_NONROT, q);
+
         dm_table_set_integrity(t);
 
         /*