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=-7.0 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 7AF9FC433DF for ; Tue, 4 Aug 2020 05:04:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 827B120792 for ; Tue, 4 Aug 2020 05:04:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726797AbgHDFEa (ORCPT ); Tue, 4 Aug 2020 01:04:30 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:51680 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726000AbgHDFEa (ORCPT ); Tue, 4 Aug 2020 01:04:30 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01419;MF=jiufei.xue@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0U4ikRIk_1596517464; Received: from ali-186590e05fa3.local(mailfrom:jiufei.xue@linux.alibaba.com fp:SMTPD_---0U4ikRIk_1596517464) by smtp.aliyun-inc.com(127.0.0.1); Tue, 04 Aug 2020 13:04:25 +0800 Subject: Re: [PATCH liburing 1/2] io_uring_enter: add timeout support To: Jens Axboe Cc: io-uring@vger.kernel.org, Stefan Metzmacher References: <1596017415-39101-1-git-send-email-jiufei.xue@linux.alibaba.com> <1596017415-39101-2-git-send-email-jiufei.xue@linux.alibaba.com> <0f6cdf31-fbec-d447-989d-969bb936838a@kernel.dk> <0002bd2c-1375-2b95-fe98-41ee0895141e@linux.alibaba.com> <252c29a9-9fb4-a61f-6899-129fd04db4a0@kernel.dk> <253b4df7-a35b-4d49-8cdc-c6fa24446bf9@kernel.dk> <6b635544-6cd0-742b-896f-2a6bf289189c@kernel.dk> <8be505f3-17fc-9a49-1e5e-286d61c435fa@linux.alibaba.com> <77f6f74d-fcf5-d669-52d8-5444929a980c@kernel.dk> From: Jiufei Xue Message-ID: Date: Tue, 4 Aug 2020 13:04:24 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <77f6f74d-fcf5-d669-52d8-5444929a980c@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 2020/8/4 下午12:50, Jens Axboe wrote: > On 8/3/20 7:29 PM, Jiufei Xue wrote: >> >> Hi Jens, >> On 2020/8/4 上午12:41, Jens Axboe wrote: >>> On 8/2/20 9:16 PM, Jiufei Xue wrote: >>>> Hi Jens, >>>> >>>> On 2020/7/31 上午11:57, Jens Axboe wrote: >>>>> Then why not just make the sqe-less timeout path flush existing requests, >>>>> if it needs to? Seems a lot simpler than adding odd x2 variants, which >>>>> won't really be clear. >>>>> >>>> Flushing the requests will access and modify the head of submit queue, that >>>> may race with the submit thread. I think the reap thread should not touch >>>> the submit queue when IORING_FEAT_GETEVENTS_TIMEOUT is supported. >>> >>> Ahhh, that's the clue I was missing, yes that's a good point! >>> >>>>> Chances are, if it's called with sq entries pending, the caller likely >>>>> wants those submitted. Either the caller was aware and relying on that >>>>> behavior, or the caller is simply buggy and has a case where it doesn't >>>>> submit IO before waiting for completions. >>>>> >>>> >>>> That is not true when the SQ/CQ handling are split in two different threads. >>>> The reaping thread is not aware of the submit queue. It should only wait for >>>> completion of the requests, such as below: >>>> >>>> submitting_thread: reaping_thread: >>>> >>>> io_uring_get_sqe() >>>> io_uring_prep_nop() >>>> io_uring_wait_cqe_timeout2() >>>> io_uring_submit() >>>> woken if requests are completed or timeout >>>> >>>> >>>> And if the SQ/CQ handling are in the same thread, applications should use the >>>> old API if they do not want to submit the request themselves. >>>> >>>> io_uring_get_sqe >>>> io_uring_prep_nop >>>> io_uring_wait_cqe_timeout >>> >>> Thanks, yes it's all clear to me now. I do wonder if we can't come up with >>> something better than postfixing the functions with a 2, that seems kind of >>> ugly and doesn't really convey to anyone what the difference is. >>> >>> Any suggestions for better naming? >>> >> how about io_uring_wait_cqe_timeout_nolock()? That means applications can use >> the new APIs without synchronization. > > But even applications that don't share the ring across submit/complete > threads will want to use the new interface, if supported by the kernel. > Yes, if they share, they must use it - but even if they don't, it's > likely going to be a more logical interface for them. > > So I don't think that _nolock() really conveys that very well, but at > the same time I don't have any great suggestions. > > io_uring_wait_cqe_timeout_direct()? Or we could go simpler and just call > it io_uring_wait_cqe_timeout_r(), which is a familiar theme from libc > that is applied to thread safe implementations. > > I'll ponder this a bit... > As suggested by Stefan, applications can pass a flag, say IORING_SETUP_GETEVENTS_TIMEOUT to initialize the ring to indicate they want to use the new feature. Function io_uring_wait_cqes() need to submit the timeout sqe neither the kernel is not supported nor applications do not want to use the new feature. So we do not need to add a new API. Thanks, Jiufei