linux-kernel - Re: [PATCH] CFS: Fix missing digit off in wmult table

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Date:	Wed, 18 Jul 2007 12:27:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Roman Zippel <zippel@...ux-m68k.org>, Ingo Molnar <mingo@...e.hu>,
	James Bruce <bruce@...rew.cmu.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Andrea Arcangeli <andrea@...e.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH] CFS: Fix missing digit off in wmult table

On Mon, 2007-07-16 at 10:47 -0700, Linus Torvalds wrote:
> 
> On Mon, 16 Jul 2007, Roman Zippel wrote:
> >
> > To illustrate the problem a little different: a task with a nice level -20 
> > got around 700% more cpu time (or 8 times more), now it gets 8500% more 
> > cpu time (or 86.7 times more).
> 
> Ingo, that _does_ sound excessive. 
> 
> How about trying a much less aggressive nice-level (and preferably linear, 
> not exponential)?

I actually like the extra range, it allows for a much softer punch of
background tasks even on somewhat slower boxen.

I've been testing CFS on my 1200 MHz lappy for some time and a strongly
niced kbuild leaves a very usable system. 

The old scheduler would leave the thing rather jumpy. And while CFS
fully fixes the jumpyness, I just did a nice +13 (which should be
equivalent to the old schedulers nice +19 for my HZ) and did a nice +19
kbuild and I can definitely feel the difference between them.

Early CFS versions had an pretty aggressive nice range (0.1% for +19),
and that has been toned down based on feedback. The current levels seem
to work well, at least on my boxen.

- Peter

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