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Asked: 2026-05-27T05:50:11+00:00

I have a single thread server process that watches few (around 100) sockets via

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I have a single thread server process that watches few (around 100) sockets via epoll in a loop, my question is that how to decide the optimum value of epoll_wait timeout value, since this is a single threaded process, everything is triggered off epoll_wait , if there is no activity on sockets, program remains idle, my guess is that if i give too small timeout, which causes too many epoll_wait calls there is no harm because even though my process is doing too many epoll_wait calls, it would be sitting idle otherwise, but there is another point, I run many other processes on this (8 core) box, something like 100 other process which are clients to this process, I am wondering how timeout value impacts cpu context switiching, i.e if i give too small timeout which results in many epoll_wait call will my server process be put in waiting many more times vs when I give a larger timeout value which results in fewer epoll_wait calls.

any thoughts/ideas.

Thanks

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1 Answer

  1. Editorial Team

    I believe there is no good reason to make your process wake up if it has nothing to do. Simply set the timeout to when you first need to do something. For example, if your server has a semantic of disconnecting a client after N seconds of inactivity, set the epoll timeout to the time after the first client would have to be disconnected assuming no activity. In other words, set it to:

    min{expire_time(client); for each client} – current_time

    Or, if that’s negative, you can disconnect at least one client immediately. In general, this works not only for disconnecting clients; you can abstract the above into “software timers” within your application.

    I’m failing to see this compromise you’ve mentioned. If you use a timeout any smaller than you have to, you’ll wake up before you have to, then, presumably, go back to sleep because you have nothing to do. What good does that do? On the other hand, you must not use a timeout any larger than what you have to – because that would make your program not respect the disconnect timeout policy.

    If your program is not waiting for any time-based event (like disconnecting clients), just give epoll_wait() timeout value -1, making it wait forever.

    UPDATE If you’re worried that this process being given less CPU when other processes are active, just give it lower nice value (scheduler priority). On the other hand, if you’re worried that your server process will be swapped out to disk in favour of other processes when it’s idle, it is possible to avoid swapping it out. (or you can just lower /proc/sys/vm/swappiness, affecting all processes)

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