linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Date:	Tue, 24 Apr 2007 09:08:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Gene Heskett <gene.heskett@...il.com>
Cc:	Peter Williams <pwil3058@...pond.net.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Davidsen <davidsen@....com>, Willy Tarreau <w@....eu>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr
Subject: Re: [REPORT] cfs-v4 vs sd-0.44


* Gene Heskett <gene.heskett@...il.com> wrote:

> > Gene has done some testing under CFS with X reniced to +10 and the 
> > desktop still worked smoothly for him.
> 
> As a data point here, and probably nothing to do with X, but I did 
> manage to lock it up, solid, reset button time tonight, by wanting 
> 'smart' to get done with an update session after amanda had started.  
> I took both smart processes I could see in htop all the way to -19, 
> but when it was about done about 3 minutes later, everything came to 
> an instant, frozen, reset button required lockup.  I should have 
> stopped at -17 I guess. :(

yeah, i guess this has little to do with X. I think in your scenario it 
might have been smarter to either stop, or to renice the workloads that 
took away CPU power from others to _positive_ nice levels. Negative nice 
levels can indeed be dangerous.

(Btw., to protect against such mishaps in the future i have changed the 
SysRq-N [SysRq-Nice] implementation in my tree to not only change 
real-time tasks to SCHED_OTHER, but to also renice negative nice levels 
back to 0 - this will show up in -v6. That way you'd only have had to 
hit SysRq-N to get the system out of the wedge.)

	Ingo
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