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=-7.6 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 8E8BFC433FE for ; Tue, 7 Sep 2021 06:38:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6EA4A610FE for ; Tue, 7 Sep 2021 06:38:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231429AbhIGGkE (ORCPT ); Tue, 7 Sep 2021 02:40:04 -0400 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:47848 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233050AbhIGGkD (ORCPT ); Tue, 7 Sep 2021 02:40:03 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04400;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UnYpry5_1630996735; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UnYpry5_1630996735) by smtp.aliyun-inc.com(127.0.0.1); Tue, 07 Sep 2021 14:38:56 +0800 Subject: Re: [PATCH 4/6] io_uring: let fast poll support multishot To: Pavel Begunkov , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-5-haoxu@linux.alibaba.com> <8f3046d9-d678-f755-e7af-a0e5040699ca@linux.alibaba.com> <45ccd2d3-267c-16df-c4be-c4530f50db86@gmail.com> From: Hao Xu Message-ID: Date: Tue, 7 Sep 2021 14:38:55 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <45ccd2d3-267c-16df-c4be-c4530f50db86@gmail.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 2021/9/7 上午3:09, Pavel Begunkov 写道: > On 9/6/21 6:40 PM, Hao Xu wrote: >> 在 2021/9/6 下午11:56, Pavel Begunkov 写道: >>> On 9/3/21 12:00 PM, Hao Xu wrote: >>>> For operations like accept, multishot is a useful feature, since we can >>>> reduce a number of accept sqe. Let's integrate it to fast poll, it may >>>> be good for other operations in the future. >>> >>> __io_arm_poll_handler()         | >>>    -> vfs_poll()                 | >>>                                  | io_async_task_func() // post CQE >>>                                  | ... >>>                                  | do_apoll_rewait(); >>>    -> continues after vfs_poll(),| >>>       removing poll->head of     | >>>       the second poll attempt. this(removal) only happen when there is error or it is EPOLLONESHOT    | >>> >>> >> Sorry.. a little bit confused by this case, would you mind explain a bit >> more..is the right part a system-workqueue context? and is >> do_apoll_rewait() io_poll_rewait() function? > > I meant in a broad sense. If your patches make lifetime of an accept > request to be like: > > accept() -> arm_apoll() -> apoll_func() -> accept() -> ... > -> ... (repeat many times) > > then do_apoll_rewait() is the second accept in the scheme. > > If not, and it's > > accept() -> arm_poll() -> apoll_func() -> apoll_func() -> > ... -> ? > > Then that "do_apoll_rewait()" should have been second and > other apoll_func()s. > > So, it's rather a thing to look after, but not a particular > bug. > > >>> One of the reasons for forbidding multiple apoll's is that it >>> might be racy. I haven't looked into this implementation, but >>> we should check if there will be problems from that. >>> >>> FWIW, putting aside this patchset, the poll/apoll is not in >>> the best shape and can use some refactoring. >>> >>> > [...] >