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Comment by gfd | Hacker News Reader

I wanted to see some benchmark numbers but the first hit on google returns a unresolved 150+ message github issue about how io_ring might not be better than epoll: https://github.com/axboe/liburing/issues/189

I didn't read the entire thread, but are there still implementation kinks that are being worked out or is the api ready to use now?

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Note: since Alex is a fairly gender neutral name I'm going to use they/them pronouns.

I went through and read it, and the submitter is incredibly confrontational and not at all open to feedback on the correctness of their benchmark. Also, when presented with contradictory evidence (their own benchmark where the results show io_uring is faster than epoll on other machines), they essentially dismiss it and says the other users ran their benchmark wrong, or that they can't reproduce their results on their machine, or that the other users used Boost and therefore are invalid. So not an entirely reliable criticism coming from them, in my opinion.

That’s not my take at all. Many people respond with hand waving arguments: maybe epoll is faster because the benchmark is wrong, or only one file descriptor is used (which wasn’t correct but said anyway), etc. Other people also respond saying they’ve been unable to match epoll performance when trying to add io_uring support to their libraries.

I would recommend to do your own benchmarking for whatever application you want to use it in. This might require building a prototype.

My understanding at the moment is that there is not one io-uring but every kernel version has a different implementation, and it changed quite a bit over the years. In the earlier version it just delegated all IO to an in kernel threadpool. Especially for network IO that’s not ideal, since the alternatives (epoll) didn’t require a threadpool neither in kernel nor userspace. And this probably showed up in benchmarks. The implementation changed, but I can’t really tell how now everything works for disk and network IO with out reviewing source code again.

A comprehensive changelog which explains implementation changes and bugs in different versions would be super helpful

I think io_uring more or less works as advertised now for the key thing it set out to do, but it removes one bottleneck in a larger system of network processing, so you can switch to io_uring, yet potentially without any other changes, a real world application can hit the next bottleneck due some adjacent architectural decision (or performance regressions as implementations are changed to accommodate an expanding envelope of uses).

There are a lot of rough edges in io_uring, foremost among them is it has been written, in classic Linux style, without regard to the security implications, so despite its youth it already collected four local privilege escalation CVEs. I recommend approaching it skeptically, write your own test and make sure it's actually faster in your use case.

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