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.
