linux-kernel - Re: epoll and multiple processes - eliminate unneeded process wake-ups

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Message-ID: <a69ae0325d14c39620477096383eff78@silodev.com>
Date:	Wed, 15 Jul 2015 16:07:17 +0300
From:	Madars Vitolins <m@...odev.com>
To:	<linux-kernel@...r.kernel.org>
Subject: Re: epoll and multiple processes - eliminate unneeded process
 wake-ups

Any comments?

Madars

Madars Vitolins @ 2015-07-13 15:34 rakstīja:
> 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

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