From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7DB64C76196 for ; Mon, 3 Apr 2023 08:38:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231807AbjDCIim (ORCPT ); Mon, 3 Apr 2023 04:38:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59164 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231741AbjDCIii (ORCPT ); Mon, 3 Apr 2023 04:38:38 -0400 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B2C527A98; Mon, 3 Apr 2023 01:38:35 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=ziyangzhang@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VfFpU8U_1680511110; Received: from 30.97.57.8(mailfrom:ZiyangZhang@linux.alibaba.com fp:SMTPD_---0VfFpU8U_1680511110) by smtp.aliyun-inc.com; Mon, 03 Apr 2023 16:38:31 +0800 Message-ID: <1d74e886-89af-bbbb-9bae-37d20ce07fb2@linux.alibaba.com> Date: Mon, 3 Apr 2023 16:38:30 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH V5 16/16] block: ublk_drv: apply io_uring FUSED_CMD for supporting zero copy Content-Language: en-US To: Ming Lei Cc: linux-kernel@vger.kernel.org, Miklos Szeredi , Xiaoguang Wang , Bernd Schubert , Pavel Begunkov , io-uring@vger.kernel.org, Stefan Hajnoczi , linux-block@vger.kernel.org, Jens Axboe , Dan Williams References: <20230328150958.1253547-1-ming.lei@redhat.com> <20230328150958.1253547-17-ming.lei@redhat.com> <2e3c20e0-a0be-eaf3-b288-c3c8fa31d1fa@linux.alibaba.com> <08b047a8-c577-a717-81a8-db8fca8ebab6@linux.alibaba.com> From: Ziyang Zhang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 2023/3/29 18:52, Ming Lei wrote: > On Wed, Mar 29, 2023 at 06:01:16PM +0800, Ziyang Zhang wrote: >> On 2023/3/29 17:00, Ming Lei wrote: >>> On Wed, Mar 29, 2023 at 10:57:53AM +0800, Ziyang Zhang wrote: >>>> On 2023/3/28 23:09, Ming Lei wrote: >>>>> Apply io_uring fused command for supporting zero copy: >>>>> >>>> >>>> [...] >>>> >>>>> >>>>> @@ -1374,7 +1533,12 @@ static int ublk_ch_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags) >>>>> if (!ubq || ub_cmd->q_id != ubq->q_id) >>>>> goto out; >>>>> >>>>> - if (ubq->ubq_daemon && ubq->ubq_daemon != current) >>>>> + /* >>>>> + * The fused command reads the io buffer data structure only, so it >>>>> + * is fine to be issued from other context. >>>>> + */ >>>>> + if ((ubq->ubq_daemon && ubq->ubq_daemon != current) && >>>>> + (cmd_op != UBLK_IO_FUSED_SUBMIT_IO)) >>>>> goto out; >>>>> >>>> >>>> Hi Ming, >>>> >>>> What is your use case that fused io_uring cmd is issued from another thread? >>>> I think it is good practice to operate one io_uring instance in one thread >>>> only. >>> >>> So far we limit io command has to be issued from the queue context, >>> which is still not friendly from userspace viewpoint, the reason is >>> that we can't get io_uring exit notification and ublk's use case is >>> very special since the queued io command may not be completed forever, >> >> OK, so UBLK_IO_FUSED_SUBMIT_IO is guaranteed to be completed because it is >> not queued. FETCH_REQ and COMMIT_AMD_FETCH are queued io commands and could >> not be completed forever so they have to be issued from ubq_daemon. Right? > > Yeah, any io command should be issued from ubq daemon context. > >> >> BTW, maybe NEED_GET_DATA can be issued from other context... > > So far it won't be supported. > > As I mentioned in the link, if io_uring can provide io_uring exit > callback, we may relax this limit. > Hi, Ming Sorry, I do not understand... I think UBLK_IO_NEED_GET_DATA is normal IO just like UBLK_IO_FUSED_SUBMIT_IO. It is issued from one pthread(ubq_daemon for now) and is completed just in time(not queued). So I think we can allow UBLK_IO_NEED_GET_DATA to be issued from other context.