[dm-devel] [PATCH 1/5] block: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE

[Bart Van Assche]

On Wed, 2017-09-20 at 00:04 +0800, Ming Lei wrote:
> Run queue at end_io is definitely wrong, because blk-mq has SCHED_RESTART
> to do that already.

Sorry but I disagree. If SCHED_RESTART is set that causes the blk-mq core to
reexamine the software queues and the hctx dispatch list but not the requeue
list. If a block driver returns BLK_STS_RESOURCE then requests end up on the
requeue list. Hence the following code in scsi_end_request():

	if (scsi_target(sdev)->single_lun || !list_empty(&sdev->host->starved_list))
		kblockd_schedule_work(&sdev->requeue_work);
	else
		blk_mq_run_hw_queues(q, true);

Bart.