epoll and multiple processes - eliminate unneeded process wake-ups

Madars Vitolins
2015-07-13T12:42:24Z

Hi Folks,

I am developing kind of open systems application, which uses multiple
processes/executables where each of them monitors some set of resources
(in this case POSIX Queues) via epoll interface. For example when 10
processes on same queue are in state of epoll_wait() and one message
arrives, all 10 processes gets woken up and all of them tries to read
the message from Q. One succeeds, the others gets EAGAIN error. The
problem is with those others, which generates extra context switches -
useless CPU usage. With more processes inefficiency gets higher.

I tried to use EPOLLONESHOT, but no help. Seems this is suitable for
multi-threaded application and not for multi-process application.

Ideal mechanism for this would be:
1. If multiple epoll sets in kernel matches same event and one or more
processes are in state of epoll_wait() - then send event only to one
waiter.
2. If none of processes are in wait state, then send the event to all
epoll sets (as it is currently). Then the first free process will grab
the event.

How do you think, would it be real to implement this? How about
concurrency?
Can you please give me some hints from which points in code to start to
implement these changes?

Thanks a lot in advance,
Madars