[throwaway81523]

Tie difference between select and epoll is just that select sets a bitmap of file descriptors, so if you are listening on 5000 sockets, you then have to scan the resulting bitmap (80 or so 64-bit ints) to find the active ones, while epoll gives you an event-like structure telling you something has happened on file descriptor N, which you can then go and check, without having to scan a bitmap. So that is more efficient if you have a lot (thousands) of active fd's. I don't remember for sure but select may actually have a limit of 1024 fd's or something like that. So epoll was preferred over select for high levels of concurrency, before io_uring arrived. But, select worked ok for the purpose and epoll was simply a refinement, not a game changer. Scanning a few hundred words of memory is not that slow, as it will all be cached anyway.