Messages in this thread | | | Subject | Re: [PATCH 7/8] mq-deadline: add blk-mq adaptation of the deadline IO scheduler | From | Jens Axboe <> | Date | Mon, 16 Jan 2017 18:47:18 -0800 |
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On 12/22/2016 09:07 AM, Paolo Valente wrote: > >> Il giorno 17 dic 2016, alle ore 01:12, Jens Axboe <axboe@fb.com> 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> >> --- > > ... > >> 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
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