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Date: Tue, 17 Apr 2007 15:32:56 -0700
From: William Lee Irwin III <wli@holomorphy.com>
To: Matt Mackall <mpm@selenic.com>
Cc: Ingo Molnar <mingo@elte.hu>, Davide Libenzi <davidel@xmailserver.org>,
       Nick Piggin <npiggin@suse.de>, Peter Williams <pwil3058@bigpond.net.au>,
       Mike Galbraith <efault@gmx.de>, Con Kolivas <kernel@kolivas.org>,
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       Andrew Morton <akpm@linux-foundation.org>,
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       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]
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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