linux-kernel - Re: Network slowdown due to CFS

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Message-ID: <20070926101851.GC2993@elte.hu>
Date:	Wed, 26 Sep 2007 12:18:51 +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,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: Network slowdown due to CFS


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

> * Ingo Molnar <mingo@...e.hu> [2007-09-26 11:47]:
> > > this will gather a good deal of info about the workload in question. 
> > > Please send me the resulting debug file.
> > Another thing: please also do the same with the vanilla v2.6.22 kernel, 
> > and send me that file too. (so that the two cases can be compared)
> 
> I put the log files here:
> http://www.cyrius.com/tmp/2.6.22
> http://www.cyrius.com/tmp/2.6.23-rc8-sched-devel
> 
> I increased the time ipfer ran to 30 secs since your script runs for
> over 15 secs.  I got:
> 
> [  3]  0.0-30.0 sec    331 MBytes  92.6 Mbits/sec   2.6.22
> vs
> [  3]  0.0-30.0 sec    222 MBytes  62.1 Mbits/sec   2.6.23-rc8-sched-devel

thanks!

the test does almost no context switches:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 2  0      0 462928   3280  37216    0    0   137    75 2306   83 13 38 47  2
 2  0      0 462928   3280  37216    0    0     0     0 8600   54  6 94  0  0
 2  0      0 462928   3280  37216    0    0     0    36 8667   55  7 93  0  0
 2  0      0 462928   3280  37216    0    0     0     0 8592   53  5 95  0  0
 2  0      0 462928   3280  37216    0    0     0     0 8638   52  7 93  0  0

(the 'cs' column shows 50-80 context switches per second.)

so there must be some other side-effect, not raw scheduling overhead or 
some other direct scheduler performance problem.

	Ingo
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