From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ming Lei Subject: Re: [PATCH 1/5] block: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE Date: Wed, 20 Sep 2017 09:19:26 +0800 Message-ID: <20170920011925.GB23062@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> <1505839754.2671.42.camel@wdc.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1505839754.2671.42.camel@wdc.com> Sender: linux-block-owner@vger.kernel.org To: Bart Van Assche Cc: "snitzer@redhat.com" , "linux-block@vger.kernel.org" , "hch@infradead.org" , "sagi@grimberg.me" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "axboe@fb.com" , "linux-nvme@lists.infradead.org" , "jejb@linux.vnet.ibm.com" , "loberman@redhat.com" , "dm-devel@redhat.com" List-Id: linux-scsi@vger.kernel.org On Tue, Sep 19, 2017 at 04:49:15PM +0000, Bart Van Assche wrote: > 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); Let's focus on dm-rq. I have explained before, dm-rq is different with SCSI's, we don't need to requeue request any more in dm-rq if blk_get_request() returns NULL in multipath_clone_and_map(), since SCHED_RESTART can cover that definitely. Not mention dm_mq_delay_requeue_request() will run the queue explicitly if it has to be done. That needn't SCHED_RESTART to cover, right? -- Ming