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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 AFB6FC2BA83 for ; Fri, 14 Feb 2020 12:52:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8242B2168B for ; Fri, 14 Feb 2020 12:52:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nCeKoA6U" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728083AbgBNMwH (ORCPT ); Fri, 14 Feb 2020 07:52:07 -0500 Received: from mail-lf1-f46.google.com ([209.85.167.46]:41504 "EHLO mail-lf1-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728062AbgBNMwH (ORCPT ); Fri, 14 Feb 2020 07:52:07 -0500 Received: by mail-lf1-f46.google.com with SMTP id m30so6665543lfp.8 for ; Fri, 14 Feb 2020 04:52:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=AHuFgxg6ao65G+XFnKoRYjRjQZtw3Zl0IwZYrENLSD0=; b=nCeKoA6UJHhs0PYPZV8yNjeH9KC7YyUMwxGuZxc3ibnHnIUFhtj0zyVPR3cnYikeTx tFOpGoYKaQgrNCikiTVHphcFiBLrx+UIpq4BmdwgoPxYmS8z1Dvtm8Y1qGfSFYYOkj6h wR3TstuH6/VBun1DcYRuLIjaeEJKzYvbXU92XT8p9Og3vJju7XIF3CPiJI4RKP6+YEuy Z8XK3v+LuSgKLcYFJfFr/zHYLmA2IFuw7LXvSfR+yZxCxLapHfXXNuUwbfrP1uy+Wl15 YA+Dv2pU67Mo3drGeArGy6zc87u/FCtgZGhJF28aakY7/7gXZ3Oz1perLD0JwL+RKDnq qJrg== 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=AHuFgxg6ao65G+XFnKoRYjRjQZtw3Zl0IwZYrENLSD0=; b=QrFi696u5vSrBi6FtHDbi8oKnz5nrqcd06j3qjMWPKHlZgFcG/rQu193T/fLMktTKM VGXeypwTbY1g5oV63YFutDd5tL22zaVEWCgIuVpMaE2Tofv6XZygCwhI+6M1STS+urdu WwM+cAWLl8cd2J/BwT2E4nSX0yckgp7wXd3BZ6DL2Oyg8mq1/BbA7GURtEY+Ln2SdXTD cFTneR8wWLrkR2i/ZONuX/o1LdH15YfAIAsavqnxn9clL7/s9sRiVwjRD1olW/7kt12M 23z4RBF2tS2nhqsIyo7GoyVG04yAu8bZnh+OuAGhcJX0+gmt61LCUm9jhBNBBgwDclNi lFWQ== X-Gm-Message-State: APjAAAV8zCrafMIMOuUYXUS1xyee+ofqA/hfJl0n/X92MXkEW/QQ7mrA FZhk11bxhcA7II6Jv3dt6ut2ZyHzIRM= X-Google-Smtp-Source: APXvYqy0kxXzPsHMq1WBP+ZLW47kwc+M496U59iudag8ACB0x72YO5eQuAVJxjzjjeeLoXws9docpw== X-Received: by 2002:a19:ca0e:: with SMTP id a14mr1645766lfg.186.1581684724448; Fri, 14 Feb 2020 04:52:04 -0800 (PST) Received: from [172.31.190.83] ([86.57.146.226]) by smtp.gmail.com with ESMTPSA id h10sm3523983ljc.39.2020.02.14.04.52.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Feb 2020 04:52:03 -0800 (PST) Subject: Re: [FEATURE REQUEST] Specify a sqe won't generate a cqe To: =?UTF-8?B?Q2FydGVyIExpIOadjumAmua0sg==?= Cc: io-uring References: <9A41C624-3D2C-40BC-A910-59CBDC5BB76E@eoitek.com> <30d88cf3-527e-4396-4934-fff13c449a80@gmail.com> <7C48911C-9C0F-42E1-90DA-7C277E37D986@eoitek.com> From: Pavel Begunkov Message-ID: <19236051-0949-ed5c-d1d5-458c07681f36@gmail.com> Date: Fri, 14 Feb 2020 15:52:02 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <7C48911C-9C0F-42E1-90DA-7C277E37D986@eoitek.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 2/14/2020 2:27 PM, Carter Li 李通洲 wrote: > >> 2020年2月14日 下午6:34，Pavel Begunkov 写道： >> >> On 2/14/2020 11:29 AM, Carter Li 李通洲 wrote: >>> To implement io_uring_wait_cqe_timeout, we introduce a magic number >>> called `LIBURING_UDATA_TIMEOUT`. The problem is that not only we >>> must make sure that users should never set sqe->user_data to >>> LIBURING_UDATA_TIMEOUT, but also introduce extra complexity to >>> filter out TIMEOUT cqes. >>> >>> Former discussion: https://github.com/axboe/liburing/issues/53 >>> >>> I’m suggesting introducing a new SQE flag called IOSQE_IGNORE_CQE >>> to solve this problem. >>> >>> For a sqe tagged with IOSQE_IGNORE_CQE flag, it won’t generate a cqe >>> on completion. So that IORING_OP_TIMEOUT can be filtered on kernel >>> side. >>> >>> In addition, `IOSQE_IGNORE_CQE` can be used to save cq size. >>> >>> For example `POLL_ADD(POLLIN)->READ/RECV` link chain, people usually >>> don’t care the result of `POLL_ADD` is ( since it will always be >>> POLLIN ), `IOSQE_IGNORE_CQE` can be set on `POLL_ADD` to save lots >>> of cq size. >>> >>> Besides POLL_ADD, people usually don’t care the result of POLL_REMOVE >>> /TIMEOUT_REMOVE/ASYNC_CANCEL/CLOSE. These operations can also be tagged >>> with IOSQE_IGNORE_CQE. >>> >>> Thoughts? >>> >> >> I like the idea! And that's one of my TODOs for the eBPF plans. >> Let me list my use cases, so we can think how to extend it a bit. >> >> 1. In case of link fail, we need to reap all -ECANCELLED, analise it and >> resubmit the rest. It's quite inconvenient. We may want to have CQE only >> for not cancelled requests. >> >> 2. When chain succeeded, you in the most cases already know the result >> of all intermediate CQEs, but you still need to reap and match them. >> I'd prefer to have only 1 CQE per link, that is either for the first >> failed or for the last request in the chain. >> >> These 2 may shed much processing overhead from the userspace. > > I couldn't agree more! > > Another problem is that io_uring_enter will be awaked for completion of > every operation in a link, which results in unnecessary context switch. > When awaked, users have nothing to do but issue another io_uring_enter > syscall to wait for completion of the entire link chain. Good point. Sounds like I have one more thing to do :) Would the behaviour as in the (2) cover all your needs? There is a nuisance with linked timeouts, but I think it's reasonable for REQ->LINKED_TIMEOUT, where it didn't fired, notify only for REQ >> >> 3. If we generate requests by eBPF even the notion of per-request event >> may broke. >> - eBPF creating new requests would also need to specify user-data, and >> this may be problematic from the user perspective. >> - may want to not generate CQEs automatically, but let eBPF do it. >> >> -- >> Pavel Begunkov > -- Pavel Begunkov