On 12/22/2016 09:07 AM, Paolo Valente wrote:

quoted

Il giorno 17 dic 2016, alle ore 01:12, Jens Axboe [off-list ref] ha scritto:

This is basically identical to deadline-iosched, except it registers
as a MQ capable scheduler. This is still a single queue design.

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

...

quoted

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
new file mode 100644
index 000000000000..3cb9de21ab21
--- /dev/null
+++ b/block/mq-deadline.c

...
+/*
+ * remove rq from rbtree and fifo.
+ */
+static void deadline_remove_request(struct request_queue *q, struct request *rq)
+{
+	struct deadline_data *dd = q->elevator->elevator_data;
+
+	list_del_init(&rq->queuelist);
+
+	/*
+	 * We might not be on the rbtree, if we are doing an insert merge
+	 */
+	if (!RB_EMPTY_NODE(&rq->rb_node))
+		deadline_del_rq_rb(dd, rq);
+

I've been scratching my head on the last three instructions, but at no
avail.  If I understand correctly, the
list_del_init(&rq->queue list);
removes rq from the fifo list.  But, if so, I don't understand how it
could be possible that rq has not been added to the rb_tree too.

Another interpretation that I tried is that the above three lines
handle correctly the following case where rq has not been inserted at
all into deadline fifo queue and rb tree: when dd_insert_request was
executed for rq, blk_mq_sched_try_insert_merge succeeded.  Yet, the
list_del_init(&rq->queue list);
does not seem to make sense.

Could you please shed some light on this for me?

I think you are correct, we don't need to touch ->queuelist for the case
where RB_EMPTY_NODE() is true. Minor detail, the list is already empty,
so it does no harm.

-- 
Jens Axboe