linux-kernel - Re: Interesting interaction between lguest and CFS

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Date:	Tue, 5 Jun 2007 09:10:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Matt Mackall <mpm@...enic.com>, akpm@...ux-foundation.org,
	Linux-kernel@...r.kernel.org
Subject: Re: Interesting interaction between lguest and CFS


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> This sounds like the waker process (nice 19) not getting a chance to 
> run.  You can hack around it for the moment by changing "nice(19)" in 
> Documentation/lguest/lguest.c to something less aggressive.

even if the waker runs at nice+19, under CFS (which schedules 
deterministically) it should not be delayed by a single nice-0 task by 
more than ~70 msecs. That is a far cry from the 'seconds' that Matt saw 
- and the sched stats he sent look anomalous too. Also, i'm not able to 
reproduce it at all - while any nice+19 related problem should be 
readily reproducable on my box too. So my current take is that this is 
some sort of host-side CFS related problem and that the lguest host 
threads somehow were the first ones that managed to trigger it in some 
really bad way.

OTOH i do agree with your patch, that nice+19 thing is quite hacky :-)

	Ingo
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