linux-kernel - Re: [PATCH] [5/6] scheduler: Protect important kernel threads against normalize

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Message-Id: <200710081433.34845.ak@suse.de>
Date:	Mon, 8 Oct 2007 14:33:34 +0200
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [5/6] scheduler: Protect important kernel threads against normalize_rt

On Monday 08 October 2007 13:51:42 Ingo Molnar wrote:
> 
> * Andi Kleen <ak@...e.de> wrote:
> 
> > Not only the migration thread, but also softlockup and stop machine 
> > need to be protected against normalize_rt(). Instead of checking for 
> > them all I added a new process flag for this.
> 
> hm, i dont really like this. The migration thread is an absolute 
> exception because it's needed for a correct scheduler. SysRq-N is like 
> SysRq-U or SysRq-B - last-minute resort in case something Goes Foul. 
> Results are not guaranteed.

softlockup is the same. Just think about it.

If you ever renormalize it and then run a fifo thread it will
starve and then eventually kill the box.

And starving CPU unplug is also equally bad.

-Andi
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