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,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,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 68076C433E0 for ; Mon, 3 Aug 2020 16:41:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E528207DF for ; Mon, 3 Aug 2020 16:41:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="ouY6593s" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726533AbgHCQlo (ORCPT ); Mon, 3 Aug 2020 12:41:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725945AbgHCQln (ORCPT ); Mon, 3 Aug 2020 12:41:43 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA6B8C06174A for ; Mon, 3 Aug 2020 09:41:42 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id t4so31632289iln.1 for ; Mon, 03 Aug 2020 09:41:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=nhpLwpoY1AwwAZejk5x5rCVH7tFjBnZ3qS3GnDixwmU=; b=ouY6593saVhWYd7EgYfvC/YSGLatOfpXGNe3WfMNdA9c9PvHnCh3HCWL/r1Zy8AfJt fcMXLJ8qGHYK0IYKlIFXrP9VPAwpgyYL1GbVY2anVRWFmnku3Wm02Y9wq6ngARQ9erbl re5C+u234ukIRv24/2cn04md9BTZLArRoZ/dTVLMPLm2camDhJpOqXXbpbe9cfB9tzQ2 6w18SPQtYwAKV82lHsvP03Q9jEBNyegRuQ9TXpPPGM/HJKnjghGilrQQB5ZgZXobZS5W tApzXvyWxzlVYpNbfsYkaWVohzfRI7WR4Wm0aFYUozxfQbnFX++kuzV55hUv0OGe4/Ek NP/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=nhpLwpoY1AwwAZejk5x5rCVH7tFjBnZ3qS3GnDixwmU=; b=gAryNNdA+4tYhGggO5Z0yuy1W//EFzRObB2ZAkvvTNBVQ28ynI+8tjIS25ak2thhX1 A/BCa+GOrQbV9KFDYNWvpUSvldLvpliIqRtJ7qWrfvnuYBtuSN0GYrGLW+xOE2H++e0a 2Qvl99BdiZdz5h048RF+bmGuFK7sK+GANPbB4VldWe6nfE/FeSk3oMMUkp2WczmAmKgL TkM1Ff3EWblIPu73yznMlz5hL9c3q+DhrF2gHGW2p4duFYvbaT1dKIvkubUxpljEpbyL gDYBENIsPNe/hAZLdhFXEbEnxYlwGxfkuCAOb1JY0feENgGUo6+ApE5g3wN7SV85Qxs8 O1KQ== X-Gm-Message-State: AOAM533GdUgoTDAzn0dbBpgNLdJ5tr/NenEbinvGg+l4skaMbUQOxyb3 kFq//QXQQLs+SPTtLCeEczx+7JexqCU= X-Google-Smtp-Source: ABdhPJwprUfBIIxDylLHlRBF5w9DaUoYfJ+7sTODIAUSuH9+ZJzBWMV5EFik4Qasout11v5xXjdcqw== X-Received: by 2002:a92:c78b:: with SMTP id c11mr229348ilk.133.1596472902009; Mon, 03 Aug 2020 09:41:42 -0700 (PDT) Received: from [192.168.1.58] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id v63sm5467750ilk.67.2020.08.03.09.41.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2020 09:41:41 -0700 (PDT) Subject: Re: [PATCH liburing 1/2] io_uring_enter: add timeout support To: Jiufei Xue Cc: io-uring@vger.kernel.org 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> From: Jens Axboe Message-ID: <6b635544-6cd0-742b-896f-2a6bf289189c@kernel.dk> Date: Mon, 3 Aug 2020 10:41:40 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: 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 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? -- Jens Axboe