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

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Message-Id: <1181002734.25878.56.camel@localhost.localdomain>
Date:	Tue, 05 Jun 2007 10:18:54 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	Linux-kernel@...r.kernel.org
Subject: Re: Interesting interaction between lguest and CFS

On Mon, 2007-06-04 at 12:37 -0500, Matt Mackall wrote:
> With 2.6.22-rc3-mm1, I've got a long-running video transcoding going
> on. In other windows, I'm compiling, reading email, etc. with no
> noticeable problems.
> 
> If I fire up lguest and leave it sitting at a shell prompt for a
> couple moments, when I return to type something at the prompt, it can
> take 2-3 seconds for my input to echo. Once it starts responding,
> typing latency disappears. Suspend the other app and the latency
> disappears.

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.

The real solution is to switch to an fd.  Fortunately, I have just such
a patch.  I am shuffling it forward in my queue now, and will send when
testing is complete...

Thanks!
Rusty.


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