Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751677AbdIMBkC (ORCPT ); Tue, 12 Sep 2017 21:40:02 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:23137 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751435AbdIMBkB (ORCPT ); Tue, 12 Sep 2017 21:40:01 -0400 Subject: Re: [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org 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> From: "jianchao.wang" Message-ID: <4b7dcb10-9ec5-9a00-8d16-009e83ef7b5b@oracle.com> Date: Wed, 13 Sep 2017 09:39:44 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170913012452.GA24642@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: aserv0021.oracle.com [141.146.126.233] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1532 Lines: 50 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); thanks jianchao