Roman Penyaev <rpenyaev@xxxxxxx> wrote: > Hi all, +cc Jason Baron > ** Limitations <snip> > 4. No support for EPOLLEXCLUSIVE > If device does not pass pollflags to wake_up() there is no way to > call poll() from the context under spinlock, thus special work is > scheduled to offload polling. In this specific case we can't > support exclusive wakeups, because we do not know actual result > of scheduled work and have to wake up every waiter. Lacking EPOLLEXCLUSIVE support is probably a showstopper for common applications using per-task epoll combined with non-blocking accept4() (e.g. nginx). Fwiw, I'm still a weirdo who prefers a dedicated thread doing blocking accept4 for distribution between tasks (so epoll never sees a listen socket). But, depending on what runtime/language I'm using, I can't always dedicate a blocking thread, so I recently started using EPOLLEXCLUSIVE from Perl5 where I couldn't rely on threads being available. If I could dedicate time to improving epoll; I'd probably add writev() support for batching epoll_ctl modifications to reduce syscall traffic, or pick-up the kevent()-like interface started long ago: https://lore.kernel.org/lkml/1393206162-18151-1-git-send-email-n1ght.4nd.d4y@xxxxxxxxx/ (but I'm not sure I want to increase the size of the syscall table).
