linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Date:	Tue, 17 Apr 2007 15:32:56 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Davide Libenzi <davidel@...ilserver.org>,
	Nick Piggin <npiggin@...e.de>,
	Peter Williams <pwil3058@...pond.net.au>,
	Mike Galbraith <efault@....de>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Huey <billh@...ppy.monkey.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

On Tue, Apr 17, 2007 at 11:24:22AM +0200, Ingo Molnar wrote:
>> yeah. If you could come up with a sane definition that also translates 
>> into low overhead on the algorithm side that would be great!

On Tue, Apr 17, 2007 at 05:08:09PM -0500, Matt Mackall wrote:
> How's this:
> If you're running two identical CPU hog tasks A and B differing only by nice
> level (Anice, Bnice), the ratio cputime(A)/cputime(B) should be a
> constant f(Anice - Bnice).
> Other definitions make things hard to analyze and probably not
> well-bounded when confronted with > 2 tasks.
> I -think- this implies keeping a separate scaled CPU usage counter,
> where the scaling factor is a trivial exponential function of nice
> level where f(0) == 1. Then you schedule based on this scaled usage
> counter rather than unscaled.
> I also suspect we want to keep the exponential base small so that the
> maximal difference is 10x-100x.

I'm already working with this as my assumed nice semantics (actually
something with a specific exponential base, suggested in other emails)
until others start saying they want something different and agree.


-- wli
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