linux-kernel - Re: Network slowdown due to CFS

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Message-ID: <20070926093445.GA24768@elte.hu>
Date:	Wed, 26 Sep 2007 11:34:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Martin Michlmayr <tbm@...ius.com>
Cc:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Network slowdown due to CFS


* Martin Michlmayr <tbm@...ius.com> wrote:

> I noticed that my network performance has gone down from 2.6.22
> from   [  3]  0.0-10.0 sec    113 MBytes  95.0 Mbits/sec
> to     [  3]  0.0-10.0 sec   75.7 MBytes  63.3 Mbits/sec
> with 2.6.23-rc1 (and 2.6.23-rc8), as measured with iperf.
> 
> I did a git bisect today and tracked it back to the commit where CFS
> was enabled ("sched: cfs core code; apply the CFS core code",
> commit dd41f596cda0d7d6e4a8b139ffdfabcefdd46528).  I also compiled a
> kernel from
> git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git
> but things don't improve.
> 
> This is on a Thecus N2100, an ARM (Intel IOP32x) based storage device 
> with a r8169 card, SATA disks and 512 MB RAM.  My config is attached.
> 
> What kind of information can I supply so you can track this down?

as a starter, could you boot the sched-devel.git kernel, with 
CONFIG_SCHED_DEBUG=y and CONFIG_SCHEDSTATS=y enabled and could you run 
this script while the iperf test is in the middle of its testrun:

  http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

this will gather a good deal of info about the workload in question. 
Please send me the resulting debug file.

	Ingo
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