使用 io_uring 进行多路复用

Question

I've recently written a simple TCP server using epoll, but I want to explore other mechanisms for high performance mutliplexing, to that end I came across io_uring, and am planning on making another simple TCP server using it.

However I read that the number of entries for io_uring is limited to 4096 in here https://kernel.dk/io_uring.pdf , which seems to imply that I won't be able to theoretically have more than that number of persistent connections.

To my understanding where normally I'd use something like epoll_wait() to wait on an event for epoll, I instead submit a specific request in io_uring and am notified when the request has completed/failed, so does that mean I can submit up to 4096 read() requests for example?

Have I misunderstood the use case of io_uring or have I misunderstood how to use it?

Answer 1

In the same document I linked, it says:

Normally an application would ask for a ring of a given size, and the assumption may be that this size corresponds directly to how many requests the application can have pending in the kernel. However, since the sqe lifetime is only that of the actual submission of it, it's possible for the application to drive a higher pending request count than the SQ ring size would indicate.

Which is precisely what you'd do for the case of listening for messages on lots of sockets - it's just that the upper limit of how many submissions you can send at once is 4096.