Date: Wed, 26 Sep 2007 13:21:37 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Martin Michlmayr <tbm@cyrius.com>
Cc: Mike Galbraith <efault@gmx.de>,
       Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org
Subject: Re: Network slowdown due to CFS
Message-ID: <20070926112137.GA13876@elte.hu>
References: <20070926085202.GE3337@deprecation.cyrius.com> <1190802208.7318.5.camel@Homer.simpson.net> <20070926104814.GM3337@deprecation.cyrius.com>
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* Martin Michlmayr <tbm@cyrius.com> wrote:

> * Mike Galbraith <efault@gmx.de> [2007-09-26 12:23]:
> > I noticed on the iperf website a patch which contains sched_yield().
> > http://dast.nlanr.net/Projects/Iperf2.0/patch-iperf-linux-2.6.21.txt
> > 
> > Do you have that patch applied by any chance?  If so, it might be a
> > worth while to try it without it.
> 
> Yes, this patch was applied.  When I revert it, I get the same (high) 
> performance with both kernels.

great! Could you try this too:

   echo 1 > /proc/sys/kernel/sched_compat_yield

does it fix iperf performance too (with the yield patch applied to 
iperf)?

I think the real fix would be for iperf to use blocking network IO 
though, or maybe to use a POSIX mutex or POSIX semaphores.

	Ingo
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