On 5/3/23 2:58?AM, Ben Noordhuis wrote: > On Tue, May 2, 2023 at 2:51?PM Pavel Begunkov <asml.silence@xxxxxxxxx> 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. -- Jens Axboe
