From: greg@kroah.com (Greg KH)
To: kernelnewbies@lists.kernelnewbies.org
Subject: epoll improvements
Date: Thu, 16 Oct 2014 14:17:59 +0200 [thread overview]
Message-ID: <20141016121759.GA28008@kroah.com> (raw)
In-Reply-To: <trinity-842dea81-708d-4ef5-86ad-68daf6f7d7e5-1413461344834@3capp-mailcom-bs07>
On Thu, Oct 16, 2014 at 02:09:05PM +0200, Nev Ikte wrote:
> Hi,
>
> I've a server using epoll and I've noticed that when
> the traffic is low, the epoll_wait() latency goes up.
>
> I've tried to reproduce it with a single client
> and basically, if ep_poll() is able to find an event or the timeout is 0,
> the latency is down to 5usec, otherwise if it enters the waitqueue
> the latency goes up to 10-25usec, which impact the application performance.
>
> Looking at the code there is something like a todo ("Is it worth to try to dig for events ?")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/eventpoll.c?id=refs/tags/v3.17#n1650
>
> Anyone knows how the situation can be improved?
> in theory having something like a 50usec spin loop
> checking for events before entering in the waitqueue should improve the situation.
>
> suggestion? patches?
The epoll code is subtle, tricky, and very very difficult to modify. I
suggest trying your suggestion and seeing if it helps any. But be
prepared to go down a long rabbit-hole in this area of the kernel.
Enjoy the trip! :)
greg k-h
next prev parent reply other threads:[~2014-10-16 12:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-16 12:09 epoll improvements Nev Ikte
2014-10-16 12:17 ` Greg KH [this message]
2014-10-16 12:48 ` Jason Ball
2014-10-16 17:02 ` Valdis.Kletnieks at vt.edu
2014-10-17 16:47 ` michi1 at michaelblizek.twilightparadox.com
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