From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 13 Sep 2017 09:52:27 +0800 From: Ming Lei To: "jianchao.wang" Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued Message-ID: <20170913015221.GB24642@ming.t460p> References: <1505236475-9209-1-git-send-email-jianchao.w.wang@oracle.com> <20170912102302.GC15792@ming.t460p> <23b700aa-ed37-1081-d980-4073804f293b@oracle.com> <20170913012452.GA24642@ming.t460p> <4b7dcb10-9ec5-9a00-8d16-009e83ef7b5b@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <4b7dcb10-9ec5-9a00-8d16-009e83ef7b5b@oracle.com> List-ID: On Wed, Sep 13, 2017 at 09:39:44AM +0800, jianchao.wang wrote: > > > On 09/13/2017 09:24 AM, Ming Lei wrote: > > On Wed, Sep 13, 2017 at 09:01:25AM +0800, jianchao.wang wrote: > >> Hi ming > >> > >> On 09/12/2017 06:23 PM, Ming Lei wrote: > >>>> @@ -1029,14 +1029,20 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list) > >>>> if (list_empty(list)) > >>>> bd.last = true; > >>>> else { > >>>> - struct request *nxt; > >>>> - > >>>> nxt = list_first_entry(list, struct request, queuelist); > >>>> bd.last = !blk_mq_get_driver_tag(nxt, NULL, false); > >>>> } > >>>> > >>>> ret = q->mq_ops->queue_rq(hctx, &bd); > >>>> if (ret == BLK_STS_RESOURCE) { > >>>> + /* > >>>> + * If an I/O scheduler has been configured and we got a > >>>> + * driver tag for the next request already, free it again. > >>>> + */ > >>>> + if (!list_empty(list)) { > >>>> + nxt = list_first_entry(list, struct request, queuelist); > >>>> + blk_mq_put_driver_tag(nxt); > >>>> + } > >>> The following way might be more simple and clean: > >>> > >>> if (nxt) > >>> blk_mq_put_driver_tag(nxt); > >>> > >>> meantime 'nxt' need to be cleared inside the 'if (list_empty(list))' > >>> before .queue_rq(). > >> > >> I had ever thought about that, but to avoid add extra command in the > >> fast path, I made the patch above. > > > > Got it, so how about changing to the following way simply: > > > > if (nxt && !list_empty(list)) > > blk_mq_put_driver_tag(nxt); > > > It seems that we even could change it as following: > if (!list_empty(list)) > blk_mq_put_driver_tag(nxt); Yeah, that is definitely more clean, :-) Feel free to add "Reviewed-by: Ming Lei " in your next post. -- Ming