From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bart.VanAssche@wdc.com (Bart Van Assche)
Date: Tue, 19 Sep 2017 16:49:15 +0000
Subject: [PATCH 1/5] block: don't call blk_mq_delay_run_hw_queue() in case
 of BLK_STS_RESOURCE
In-Reply-To: <20170919160401.GC19830@ming.t460p>
References: <20170915164456.9803-1-ming.lei@redhat.com>
 <20170915164456.9803-2-ming.lei@redhat.com>
 <1505498249.3420.15.camel@wdc.com> <20170917124000.GB6289@ming.t460p>
 <1505747894.2685.6.camel@wdc.com> <20170919054308.GA2517@ming.t460p>
 <1505835394.2671.18.camel@wdc.com> <20170919155603.GB22809@redhat.com>
 <20170919160401.GC19830@ming.t460p>
Message-ID: <1505839754.2671.42.camel@wdc.com>

On Wed, 2017-09-20@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.