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[72.132.29.68]) by smtp.gmail.com with ESMTPSA id 126sm8384398pfv.72.2021.09.06.09.42.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Sep 2021 09:42:16 -0700 (PDT) Subject: Re: [PATCH 6/6] io_uring: enable multishot mode for accept To: Pavel Begunkov , Hao Xu 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> From: Jens Axboe Message-ID: <0328b6fe-9100-1ae4-e3cc-9dccc36ed141@kernel.dk> Date: Mon, 6 Sep 2021 10:42:13 -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 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 9/6/21 9:32 AM, Pavel Begunkov wrote: > On 9/6/21 1:35 PM, 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 > > We still have 2 bits left, and IIRC you wanted to take only 1 of them. > We don't need extending it at the moment, it sounded to me like a plan > for the future. No extra trouble for now Right, and it should be a separate thing anyway. But as you say, there's still 2 bits left, this is more about longer term planning than this particular patchset. > Anyway, I can't think of many requests working in this mode, and I think > sqe_flags should be taken only for features applicable to all (~most) of > requests. Maybe we'd better to fit it individually into accept in the > end? Sounds more plausible tbh That's why I suggested making it op private instead, I don't particularly like having io_uring wide flags that are only applicable to a (very) small subset of requests. And there's also precedence here already in terms of poll supporting mshot with a private flag. -- Jens Axboe