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[188.31.116.198]) by smtp.gmail.com with ESMTPSA id j6-20020a5d6186000000b003063772a55bsm4737287wru.61.2023.05.03.06.23.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 May 2023 06:23:12 -0700 (PDT) Message-ID: <73b4fc31-9832-adbb-4537-87ca76079f86@gmail.com> Date: Wed, 3 May 2023 14:21:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH] io_uring: undeprecate epoll_ctl support Content-Language: en-US To: Jens Axboe , Ben Noordhuis Cc: io-uring@vger.kernel.org References: <20230501185240.352642-1-info@bnoordhuis.nl> From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 5/3/23 13:49, Jens Axboe wrote: > On 5/3/23 2:58?AM, Ben Noordhuis wrote: >> On Tue, May 2, 2023 at 2:51?PM Pavel Begunkov wrote: >>> >>> On 5/1/23 19:52, Ben Noordhuis wrote: >>>> Libuv recently started using it so there is at least one consumer now. >>> >>> It was rather deprecated because io_uring controlling epoll is a bad >>> idea and should never be used. One reason is that it means libuv still >>> uses epoll but not io_uring, and so the use of io_uring wouldn't seem >>> to make much sense. You're welcome to prove me wrong on that, why libuv >>> decided to use a deprecated API in the first place? >>> Sorry, but the warning is going to stay and libuv should revert the use >>> of epol_ctl requests. >> >> Why use a deprecated API? Because it was only recently deprecated. >> Distro kernels don't warn about it yet. I only found out because of >> kernel source code spelunking. >> >> Why combine io_uring and epoll? Libuv uses level-triggered I/O for >> reasons (I can go into detail but they're not material) so it's very >> profitable to batch epoll_ctl syscalls; it's the epoll_ctlv() syscall >> people have been asking for since practically forever. >> >> Why not switch to io_uring wholesale? Libuv can't drop support for >> epoll because of old kernels, and io_uring isn't always clearly faster >> than epoll in the first place. >> >> As to the warning: according to the commit that introduced it, it was >> added because no one was using IORING_OP_EPOLL_CTL. Well, now someone >> is using it. Saying it's a bad API feels like post-hoc >> rationalization. I kindly ask you merge this patch. I'd be happy to >> keep an eye on io_uring/epoll.c if you're worried about maintenance >> burden. > > This is obviously mostly our fault, as the deprecation patch should've > obviously been backported to stable. Just adding it to the current > kernel defeated the purpose, as it added a long period where older > kernels quite happily accepted epoll use cases. > > So I do agree, the only sane course of action here is to un-deprecate > it. nack, keeping piling rubbish is not a great course of action at all. Has libuv already released it? Because it seems the patches were just merged. -- Pavel Begunkov