Date: Sat, 12 Jul 2003 13:48:21 -0700 (PDT)
From: Davide Libenzi <davidel@xmailserver.org>
To: Eric Varsanyi <e0206@foo21.com>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Davide Libenzi <davidel@xmailserver.org>
Subject: Re: [Patch][RFC] epoll and half closed TCP connections
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Message-ID: <Pine.LNX.4.55.0307121346140.4720@bigblue.dev.mcafeelabs.com>
References: <20030712181654.GB15643@srv.foo21.com> <20030712194432.GE10450@mail.jlokier.co.uk>
 <20030712205114.GC15643@srv.foo21.com>
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On Sat, 12 Jul 2003, Eric Varsanyi wrote:

> > > In a level triggered world this all just works because the read ready
> > > indication is driven back to the app as long as the socket state is half
> > > closed. The event driven epoll mechanism folds these two indications
> > > together and thus loses one 'edge'.
> >
> > Well then, use epoll's level-triggered mode.  It's quite easy - it's
> > the default now. :)
>
> The problem with all the level triggered schemes (poll, select, epoll w/o
> EPOLLET) is that they call every driver and poll status for every call into
> the kernel. This appeared to be killing my app's performance and I verified
> by writing some simple micro benchmarks.

Look this is false for epoll. Given N fds inside the set and M hot/ready
fds, epoll scale O(M) and not O(N) (like poll/select). There's a huge
difference, expecially with real loads.


- Davide

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