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

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Date:	Tue, 17 Jul 2007 09:53:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Matt Mackall <mpm@...enic.com>, James Bruce <bruce@...rew.cmu.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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

* Roman Zippel <zippel@...ux-m68k.org> wrote:

> > > It's nice that these artifacts are gone, but that still doesn't 
> > > explain why this ratio had to be increase that much from around 
> > > 1:10 to 1:69.
> > 
> > More dynamic range is better? If you actually want a task to get 20x 
> > the CPU time of another, the older scheduler doesn't really allow 
> > it.
> 
> You can already have that, the complete range level from 19 to -20 was 
> about 1:80.

But that is irrelevant: all tasks start out at nice 0, and what matters 
is the dynamic range around 0.

So the dynamic range has been made uniform in the positive from 
1:10...1:20...1:30 to 1:69 for nice +19, and from 1:8 to 1:69 in the 
minus. (with 1:86 nice -20) If you look at the negative nice levels 
alone it's a substantial increase but if you compare it with positive 
nice levels you'll similar kinds of dynamic ranges were already present 
in the old scheduler and you'll see why we've done it.

Negative nice levels are admin-controlled, the increase in the negative 
levels is is not a big issue and people actually like the increased 
dynamic range and the consistency. The positive range _might_ be a 
bigger issue but there we were largely inconsistent anyway, and again, 
people like the increased dynamic range.

	Ingo
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