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

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Date:	Tue, 17 Apr 2007 17:39:09 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	William Lee Irwin III <wli@...omorphy.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 03:32:56PM -0700, William Lee Irwin III wrote:
> 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.

Good. This has a couple nice mathematical properties, including
"bounded unfairness" which I mentioned earlier. What base are you
looking at?

-- 
Mathematics is the supreme nostalgia of our time.
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