linux-kernel - Re: [patch] CFS scheduler, -v18

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Date:	Sun, 24 Jun 2007 17:52:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Willy Tarreau <w@....eu>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [patch] CFS scheduler, -v18


* Willy Tarreau <w@....eu> wrote:

> Today I had a little time to try CFS again (last time it was -v9!). I 
> ran it on top of 2.6.20.14, and simply tried ocbench again. You 
> remember ? With -v9, I ran 64 processes which all progressed very 
> smoothly. With -v18, it's not the case anymore. When I run 64 
> processes, only 7 of them show smooth rounds, while all the other ones 
> are only updated once a second. Sometimes they only progress by one 
> iteration, sometimes by a full round. Some are even updated once ever 
> 2 seconds, because if I drag an xterm above them and quickly remove 
> it, the xterm leaves a trace there for up to 2 seconds.
> 
> Also, only one of my 2 CPUs is used. I see the rq vary between 1 and 
> 5, with a permanent 50% idle... :
> 
>    procs                      memory      swap          io     system      cpu
>  r  b  w   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id
>  1  0  0      0 874400   7864  90436    0    0     0     0  279  2204 50  0 50
>  3  0  0      0 874408   7864  90436    0    0     0     0  273  2122 50  1 50
>  1  0  0      0 874408   7864  90436    0    0     0     0  253  1660 49  1 50
>  3  0  0      0 874408   7864  90436    0    0     0     0  252  1977 50  0 50
>  2  0  0      0 874408   7864  90436    0    0     0     0  253  2274 49  1 50
>  3  0  0      0 874408   7864  90436    0    0     0     0  252  1846 49  1 50
>  1  0  0      0 874408   7864  90436    0    0     0     0  339  1782 49  1 50
> 
> I have no idea about what version brought that unexpected behaviour, 
> but it's clearly something which needs to be tracked down.

hm, the two problems might be related. Could you try v17 perhaps? In v18 
i have 'unified' all the sched.c's between the various kernel releases, 
maybe that brought in something unexpected on 2.6.20.14. (perhaps try 
v2.6.21.5 based cfs too?)

> My scheduler is at 250 Hz, and here are the values I found in 
> /proc/sys/kernel:

could you send me the file the cfs-debug-info.sh script produced. You 
can pick the script up from:

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

(i'd suggest to send it in private mail, output is large and detailed. 
If your kernel has no /proc/config.gz then please send me your .config 
file too.)

	Ingo
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