blk-mq: honor IO scheduler for multiqueue devices

If a device is using multiple queues, the IO scheduler may be bypassed.
This may hurt performance for some slow MQ devices, and it also breaks
zoned devices which depend on mq-deadline for respecting the write order
in one zone.

Don't bypass io scheduler if we have one setup.

This patch can double sequential write performance basically on MQ
scsi_debug when mq-deadline is applied.

Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Javier González <javier@javigon.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6e3b15f70cd7ae651bfd149115364135312aeaf2..5d4bef3c378dbfdf59191816fab5b6c604926fbb 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2012,6 +2012,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
                }
 
                blk_add_rq_to_plug(plug, rq);
+       } else if (q->elevator) {
+               blk_mq_sched_insert_request(rq, false, true, true);
        } else if (plug && !blk_queue_nomerges(q)) {
                /*
                 * We do limited plugging. If the bio can be merged, do that.
@@ -2035,8 +2037,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
                        blk_mq_try_issue_directly(data.hctx, same_queue_rq,
                                        &cookie);
                }
-       } else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
-                       !data.hctx->dispatch_busy)) {
+       } else if ((q->nr_hw_queues > 1 && is_sync) ||
+                       !data.hctx->dispatch_busy) {
                blk_mq_try_issue_directly(data.hctx, rq, &cookie);
        } else {
                blk_mq_sched_insert_request(rq, false, true, true);