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[66.29.188.166]) by smtp.gmail.com with ESMTPSA id l22sm3125490pfj.179.2018.12.06.19.42.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Dec 2018 19:42:30 -0800 (PST) Subject: Re: [PATCH V11 0/4] blk-mq: refactor code of issue directly To: "jianchao.wang" Cc: ming.lei@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <1544152185-32667-1-git-send-email-jianchao.w.wang@oracle.com> <0adf3419-bcce-93d8-51fb-aee7cbb5ae17@oracle.com> <16205e68-aa5e-c59d-364e-4164a0e51dc7@kernel.dk> From: Jens Axboe Message-ID: <1e183b77-2c4d-71ff-b019-2b1070d2ed6b@kernel.dk> Date: Thu, 6 Dec 2018 20:42:28 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 12/6/18 8:41 PM, jianchao.wang wrote: > > > On 12/7/18 11:34 AM, Jens Axboe wrote: >> On 12/6/18 8:32 PM, Jens Axboe wrote: >>> On 12/6/18 8:26 PM, jianchao.wang wrote: >>>> >>>> >>>> On 12/7/18 11:16 AM, Jens Axboe wrote: >>>>> On 12/6/18 8:09 PM, Jianchao Wang wrote: >>>>>> Hi Jens >>>>>> >>>>>> Please consider this patchset for 4.21. >>>>>> >>>>>> It refactors the code of issue request directly to unify the interface >>>>>> and make the code clearer and more readable. >>>>>> >>>>>> This patch set is rebased on the recent for-4.21/block and add the 1st >>>>>> patch which inserts the non-read-write request to hctx dispatch >>>>>> list to avoid to involve merge and io scheduler when bypass_insert >>>>>> is true, otherwise, inserting is ignored, BLK_STS_RESOURCE is returned >>>>>> and the caller will fail forever. >>>>>> >>>>>> The 2nd patch refactors the code of issue request directly to unify the >>>>>> helper interface which could handle all the cases. >>>>>> >>>>>> The 3rd patch make blk_mq_sched_insert_requests issue requests directly >>>>>> with 'bypass' false, then it needn't to handle the non-issued requests >>>>>> any more. >>>>>> >>>>>> The 4th patch replace and kill the blk_mq_request_issue_directly. >>>>> >>>>> Sorry to keep iterating on this, but let's default to inserting to >>>>> the dispatch list if we ever see busy from a direct dispatch. I'm fine >>>>> with doing that for 4.21, as suggested by Ming, I just didn't want to >>>>> fiddle with it for 4.20. This will prevent any merging on the request >>>>> going forward, which I think is a much safer default. >>>>> >>>>> You do this already for some cases. Let's do it unconditionally for >>>>> a request that was ever subjected to ->queue_rq() and we didn't either >>>>> error or finish after the fact. >>>>> >>>> I have done it in this version if I get your point correctly. >>>> Please refer to the following fragment in the 2nd patch. >>>> >>>> + /* >>>> + * If the request is issued unsuccessfully with >>>> + * BLK_STS_DEV_RESOURCE or BLK_STS_RESOURCE, insert >>>> + * the request to hctx dispatch list due to attached >>>> + * lldd resource. >>>> + */ >>>> + force = true; >>>> + ret = __blk_mq_issue_directly(hctx, rq, cookie, last); >>>> +out_unlock: >>>> + hctx_unlock(hctx, srcu_idx); >>>> +out: >>>> + switch (ret) { >>>> + case BLK_STS_OK: >>>> + break; >>>> + case BLK_STS_DEV_RESOURCE: >>>> + case BLK_STS_RESOURCE: >>>> + if (force) { >>>> + blk_mq_request_bypass_insert(rq, run_queue); >>>> + ret = bypass ? BLK_STS_OK : ret; >>>> + } else if (!bypass) { >>>> + blk_mq_sched_insert_request(rq, false, >>>> + run_queue, false); >>>> + } >>>> + break; >>>> + default: >>> >>> You are right, I missed that you set force = true before doing the >>> issue. So this looks good to me! >> >> I applied your series. With this, we should be good to remove the >> REQ_NOMERGE logic that was added for the corruption case, and the >> blk_rq_can_direct_dispatch() as well? >> > > Yes, it should be that. > Every thing rejected by .queue_rq is ended or inserted into hctx dispatch > list. And also direct-issue path is unified with normal path. Why are we doing that return value dance, depending on whether this is a bypass insert or not? That seems confusing. -- Jens Axboe