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 F24FAC433E0 for ; Tue, 4 Aug 2020 04:50:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0313F207FC for ; Tue, 4 Aug 2020 04:50:29 +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="q68isjQe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729658AbgHDEu2 (ORCPT ); Tue, 4 Aug 2020 00:50:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52812 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726000AbgHDEu1 (ORCPT ); Tue, 4 Aug 2020 00:50:27 -0400 Received: from mail-pj1-x1042.google.com (mail-pj1-x1042.google.com [IPv6:2607:f8b0:4864:20::1042]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4F48C06174A for ; Mon, 3 Aug 2020 21:50:27 -0700 (PDT) Received: by mail-pj1-x1042.google.com with SMTP id kr4so1321919pjb.2 for ; Mon, 03 Aug 2020 21:50:27 -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=9POfZDLIBxlIfDoC/ZJdltW/SoYvRzgXK4DdlL6UmqA=; b=q68isjQejFxbHApxmWYhYrgYq4Z+ah8Z9NHkqlNqSR3GX8IHKJwdXMxvfMN0ERddOP Zw6V1r0mCKZt2b9lvTi+9koKgAPe2mUgbZwpFkTyTA7YmQXDXT/Gff36uLnDgGLllQ2G Engwwbbjqsjmjr0xRmSJ05YGdy4sc0/9duxQprk3MYiwttY6WgC8Lh4hwdUZN1wzoxax F1/uwEv3mDbsvBrQKkTchr6HaVd8i6rMfFJy8ssWIw3oda1sj5Hjfc5Kya1gHA6szXl2 IDyyKXM14oWmcaySD/twQudFAZU/g76KfyCei5Lf3o1wsTCuQ7iINsy/D0lzkOCEpTur 4fBw== 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=9POfZDLIBxlIfDoC/ZJdltW/SoYvRzgXK4DdlL6UmqA=; b=EyO5tKWfUdtsnT2Rx3uHBavrIZpWt1Vm0mDqmO7JlVZrFz5ybrmNodT945UTtJETj5 pcvlGDe+gWbFYUisVrongURcevPT+SCgr69icvCt7cXqKiEKBcfceHgwH3gIPi+QYUjJ k4sWP5DAjiVgQHdNnpqn0pEUAUOUQ6nDQx5hBuGJ3isz9wDyhIX+vhT7I8uV5w2enJvX yWAmuqAV8rCFhoKt5nj+CnhzJHRHRT8fkwV1rffnNa0LyjDcQ7otAxPGzJQ3ZNN3Wg9w Cl/94AcC7eICqbyjyJ9fpFdlS9ecXIuRZJ2j0VwKbUk49bFzEuoRe8wpQkUcQuHtKhuK VdeQ== X-Gm-Message-State: AOAM531D6BeW7AR6/PNbjMbFlwzH8703pWduovnoY4kgtG88JovE9SKo 6ZkDleNmmBYBBnEwfPWjiY/sSs8xa+g= X-Google-Smtp-Source: ABdhPJy3Yy+TbiuFFnFY3UygnynZcNw7wS1miNNxegDRWM8XH8XiXLO6JAC/V2O1YitiGEtyYZSUWg== X-Received: by 2002:a17:90a:14a5:: with SMTP id k34mr2701456pja.37.1596516626744; Mon, 03 Aug 2020 21:50:26 -0700 (PDT) Received: from [192.168.1.182] ([66.219.217.173]) by smtp.gmail.com with ESMTPSA id 12sm20695376pfn.173.2020.08.03.21.50.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2020 21:50:25 -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> <6b635544-6cd0-742b-896f-2a6bf289189c@kernel.dk> <8be505f3-17fc-9a49-1e5e-286d61c435fa@linux.alibaba.com> From: Jens Axboe Message-ID: <77f6f74d-fcf5-d669-52d8-5444929a980c@kernel.dk> Date: Mon, 3 Aug 2020 22:50:24 -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: <8be505f3-17fc-9a49-1e5e-286d61c435fa@linux.alibaba.com> 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 8/3/20 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... -- Jens Axboe