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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38556C433ED for ; Thu, 8 Apr 2021 11:43:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E7A2B61155 for ; Thu, 8 Apr 2021 11:43:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230491AbhDHLn5 (ORCPT ); Thu, 8 Apr 2021 07:43:57 -0400 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:32907 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231239AbhDHLn4 (ORCPT ); Thu, 8 Apr 2021 07:43:56 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=alimailimapcm10staff010182156082;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UUu2Msn_1617882223; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UUu2Msn_1617882223) by smtp.aliyun-inc.com(127.0.0.1); Thu, 08 Apr 2021 19:43:44 +0800 Subject: Re: [PATCH 5.13 v2] io_uring: maintain drain requests' logic From: Hao Xu To: Jens Axboe Cc: io-uring@vger.kernel.org, Pavel Begunkov , Joseph Qi References: <1617794605-35748-1-git-send-email-haoxu@linux.alibaba.com> <00898a9b-d2f2-1108-b9d9-2d6acea6e713@kernel.dk> <32f812e1-c044-d4b3-d26f-3721e4611a1d@linux.alibaba.com> Message-ID: <119436dd-5e55-9812-472c-7a257bda12fb@linux.alibaba.com> Date: Thu, 8 Apr 2021 19:43:43 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <32f812e1-c044-d4b3-d26f-3721e4611a1d@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 在 2021/4/8 下午6:16, Hao Xu 写道: > 在 2021/4/7 下午11:49, Jens Axboe 写道: >> On 4/7/21 5:23 AM, Hao Xu wrote: >>> more tests comming, send this out first for comments. >>> >>> Hao Xu (3): >>>    io_uring: add IOSQE_MULTI_CQES/REQ_F_MULTI_CQES for multishot >>> requests >>>    io_uring: maintain drain logic for multishot requests >>>    io_uring: use REQ_F_MULTI_CQES for multipoll IORING_OP_ADD >>> >>>   fs/io_uring.c                 | 34 +++++++++++++++++++++++++++++----- >>>   include/uapi/linux/io_uring.h |  8 +++----- >>>   2 files changed, 32 insertions(+), 10 deletions(-) >> >> Let's do the simple cq_extra first. I don't see a huge need to add an >> IOSQE flag for this, probably best to just keep this on a per opcode >> basis for now, which also then limits the code path to just touching >> poll for now, as nothing else supports multishot CQEs at this point. >> > gotcha. > a small issue here: >  sqe-->sqe(link)-->sqe(link)-->sqe(link, multishot)-->sqe(drain) > > in the above case, assume the first 3 single-shot reqs have completed. > then I think the drian request won't be issued now unless the multishot > request in the linkchain has been issued. The trick is: a multishot req > in a linkchain consumes cached_sq_head when io_get_sqe(), which means it > is counted in seq, but we will deduct the sqe when it is issued if we > want to do the job per opcode not in the main code path. > before the multishot req issued: >      all_sqes(4) - multishot_sqes(0) == all_cqes(3) - multishot_cqes(0) > after the multishot req issued: >      all_sqes(4) - multishot_sqes(1) == all_cqes(3) - multishot_cqes(0) Sorry, my statement is wrong. It's not "won't be issued now unless the multishot request in the linkchain has been issued". Actually I now think the drain req won't be issued unless the multishot request in the linkchain has completed. Because we may first check req_need_defer() then issue(req->link), so: sqe0-->sqe1(link)-->sqe2(link)-->sqe3(link, multishot)-->sqe4(drain) sqe2 is completed: call req_need_defer: all_sqes(4) - multishot_sqes(0) == all_cqes(3) - multishot_cqes(0) sqe3 is issued: all_sqes(4) - multishot_sqes(1) == all_cqes(3) - multishot_cqes(0) sqe3 is completed: call req_need_defer: all_sqes(4) - multishot_sqes(1) == all_cqes(3) - multishot_cqes(0) sqe4 shouldn't wait sqe3.