3 ms·

Looks like a little bit of both. Linux has a lot to catch up because epoll is a mess. It is limited to file descriptors with a readiness semantic (sockets, pipe

by crest 7y ago

Looks like a little bit of both. Linux has a lot to catch up because epoll is a mess. It is limited to file descriptors with a readiness semantic (sockets, pipes, ttys) meaning that it will never work with normal files because they are always ready while blocking whenever they feel like it. The second API fuck up is the fork/exec semantic. Oh and they tried to get away with edge triggered instead of level triggered. All in all epoll is a just a nasty case of NIH. The epoll developers just wrote code without understanding the prior art in their field (e.g. kqueue).

AnanasAttack 7y ago
What do you dislike about edge triggered mode?
oralty 7y ago
epoll (and even kqueue) is not aio and was never intended as such. While epoll had some early snafus, those have long been fixed (offering ET and LT) and it works well for its intended purpose (io readiness). This (io_uring) is more for a thing like Windows overlapped IO and "unix" (incl FreeBSD) aio. AIO on linux is yet a separate set of syscalls (io_*) and has since day one in the 2.5 days been pretty much a useless joke, very limited in scope (O_DIRECT only). kqueue is neither epoll nor aio but a common queueing interface for events, which includes io readiness and aio completion as separate types. Linux prefers to split these as different types of fds. FWIW, this wasn't due to obliviousness of the existing design - https://yarchive.net/comp/linux/event_queues.html https://yarchive.net/comp/linux/event_queues.html. Honestly your comment sounds very like a regurgitated old and somewhat outdated Bryan Cantrill rant.
- gpderetta 7y ago
  The link doesn't explain much. The only argument that Linus has on kqueue is that is overengineered. Then it goes on a long multi message rant in how having multiple queues is insane. Luckily, in the end epoll ended up supporting multiple queues at least. I do believe that ET is good though.

by crest 7y ago

AnanasAttack 7y ago

What do you dislike about edge triggered mode?

oralty 7y ago

epoll (and even kqueue) is not aio and was never intended as such. While epoll had some early snafus, those have long been fixed (offering ET and LT) and it works well for its intended purpose (io readiness). This (io_uring) is more for a thing like Windows overlapped IO and "unix" (incl FreeBSD) aio. AIO on linux is yet a separate set of syscalls (io_*) and has since day one in the 2.5 days been pretty much a useless joke, very limited in scope (O_DIRECT only). kqueue is neither epoll nor aio but a common queueing interface for events, which includes io readiness and aio completion as separate types. Linux prefers to split these as different types of fds. FWIW, this wasn't due to obliviousness of the existing design - https://yarchive.net/comp/linux/event_queues.html https://yarchive.net/comp/linux/event_queues.html. Honestly your comment sounds very like a regurgitated old and somewhat outdated Bryan Cantrill rant.

gpderetta 7y ago
The link doesn't explain much. The only argument that Linus has on kqueue is that is overengineered. Then it goes on a long multi message rant in how having multiple queues is insane. Luckily, in the end epoll ended up supporting multiple queues at least. I do believe that ET is good though.