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=-17.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 4BF7BC433F5 for ; Mon, 6 Sep 2021 15:00:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31BFD6023F for ; Mon, 6 Sep 2021 15:00:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242190AbhIFPB5 (ORCPT ); Mon, 6 Sep 2021 11:01:57 -0400 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:54083 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234783AbhIFPB4 (ORCPT ); Mon, 6 Sep 2021 11:01:56 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R991e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=haoxu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0UnVYcxJ_1630940450; Received: from B-25KNML85-0107.local(mailfrom:haoxu@linux.alibaba.com fp:SMTPD_---0UnVYcxJ_1630940450) by smtp.aliyun-inc.com(127.0.0.1); Mon, 06 Sep 2021 23:00:50 +0800 Subject: Re: [PATCH 6/6] io_uring: enable multishot mode for accept To: Jens Axboe , Pavel Begunkov Cc: io-uring@vger.kernel.org, Joseph Qi References: <20210903110049.132958-1-haoxu@linux.alibaba.com> <20210903110049.132958-7-haoxu@linux.alibaba.com> <95387504-3986-77df-7cb4-d136dd4be1ec@linux.alibaba.com> <701e50f5-2444-5b56-749b-1c1affc26ce9@gmail.com> <004fdfbb-154f-f7c4-d65b-a9c3de1a03d8@kernel.dk> From: Hao Xu Message-ID: Date: Mon, 6 Sep 2021 23:00:49 +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: <004fdfbb-154f-f7c4-d65b-a9c3de1a03d8@kernel.dk> 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 2021/9/6 下午9:31, Jens Axboe 写道: > On 9/6/21 6:35 AM, Hao Xu wrote: >> 在 2021/9/6 上午3:44, Jens Axboe 写道: >>> On 9/4/21 4:46 PM, Pavel Begunkov wrote: >>>> On 9/4/21 7:40 PM, Jens Axboe wrote: >>>>> On 9/4/21 9:34 AM, Hao Xu wrote: >>>>>> 在 2021/9/4 上午12:29, Jens Axboe 写道: >>>>>>> On 9/3/21 5:00 AM, Hao Xu wrote: >>>>>>>> Update io_accept_prep() to enable multishot mode for accept operation. >>>>>>>> >>>>>>>> Signed-off-by: Hao Xu >>>>>>>> --- >>>>>>>> fs/io_uring.c | 14 ++++++++++++-- >>>>>>>> 1 file changed, 12 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>>>>>> index eb81d37dce78..34612646ae3c 100644 >>>>>>>> --- a/fs/io_uring.c >>>>>>>> +++ b/fs/io_uring.c >>>>>>>> @@ -4861,6 +4861,7 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags) >>>>>>>> static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>>>>>>> { >>>>>>>> struct io_accept *accept = &req->accept; >>>>>>>> + bool is_multishot; >>>>>>>> >>>>>>>> if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL)) >>>>>>>> return -EINVAL; >>>>>>>> @@ -4872,14 +4873,23 @@ static int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>>>>>>> accept->flags = READ_ONCE(sqe->accept_flags); >>>>>>>> accept->nofile = rlimit(RLIMIT_NOFILE); >>>>>>>> >>>>>>>> + is_multishot = accept->flags & IORING_ACCEPT_MULTISHOT; >>>>>>>> + if (is_multishot && (req->flags & REQ_F_FORCE_ASYNC)) >>>>>>>> + return -EINVAL; >>>>>>> >>>>>>> I like the idea itself as I think it makes a lot of sense to just have >>>>>>> an accept sitting there and generating multiple CQEs, but I'm a bit >>>>>>> puzzled by how you pass it in. accept->flags is the accept4(2) flags, >>>>>>> which can currently be: >>>>>>> >>>>>>> SOCK_NONBLOCK >>>>>>> SOCK_CLOEXEC >>>>>>> >>>>>>> While there's not any overlap here, that is mostly by chance I think. A >>>>>>> cleaner separation is needed here, what happens if some other accept4(2) >>>>>>> flag is enabled and it just happens to be the same as >>>>>>> IORING_ACCEPT_MULTISHOT? >>>>>> Make sense, how about a new IOSQE flag, I saw not many >>>>>> entries left there. >>>>> >>>>> Not quite sure what the best approach would be... The mshot flag only >>>>> makes sense for a few request types, so a bit of a shame to have to >>>>> waste an IOSQE flag on it. Especially when the flags otherwise passed in >>>>> are so sparse, there's plenty of bits there. >>>>> >>>>> Hence while it may not be the prettiest, perhaps using accept->flags is >>>>> ok and we just need some careful code to ensure that we never have any >>>>> overlap. >>>> >>>> Or we can alias with some of the almost-never-used fields like >>>> ->ioprio or ->buf_index. >>> >>> It's not a bad idea, as long as we can safely use flags from eg ioprio >>> for cases where ioprio would never be used. In that sense it's probably >>> safer than using buf_index. >>> >>> The alternative is, as has been brougt up before, adding a flags2 and >>> reserving the last flag in ->flags to say "there are flags in flags2". >>> Not exactly super pretty either, but we'll need to extend them at some >>> point. >> I'm going to do it in this way, there is another thing we have to do: >> extend req->flags too, since flags we already used > 32 if we add >> sqe->ext_flags > > As far as I can tell from a quick look, there's still plenty of flags > left for REQ_F additions, about 8 of them. Don't Ah, sorry, I realised that I reserved the 8 ext_flags bits right after the first 8 bits for sqe->flags for convenience. And that's why I though not enough space in REQ_F. Thanks. expand req->flags if we > can avoid it, just add some safeguards to ensure we don't mess up. > > Since we haven't really been tight on req->flags before, there's also > some low hanging fruit there that will allow us to reclaim some of them > if we need to. >