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.
