block: add queue flag for SSD/non-rotational devices

We don't want to idle in AS/CFQ if the device doesn't have a seek
penalty. So add a QUEUE_FLAG_NONROT to indicate a non-rotational
device, low level drivers should set this flag upon discovery of
an SSD or similar device type.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 494b6fdcb183..03a5953bb5df 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -878,6 +878,12 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
         struct cfq_io_context *cic;
         unsigned long sl;
 
+        /*
+         * SSD device without seek penalty, disable idling
+         */
+        if (blk_queue_nonrot(cfqd->queue))
+                return;
+
         WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
         WARN_ON(cfq_cfqq_slice_new(cfqq));