linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Message-ID: <20070425060531.GC19966@holomorphy.com>
Date:	Tue, 24 Apr 2007 23:05:31 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	"Li, Tong N" <tong.n.li@...el.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Davidsen <davidsen@....com>, Willy Tarreau <w@....eu>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44

On Tue, Apr 24, 2007 at 06:22:53PM -0700, Li, Tong N wrote:
> The goal of a proportional-share scheduling algorithm is to minimize the
> above metrics. If the lag function is bounded by a constant for any
> thread in any time interval, then the algorithm is considered to be
> fair. You may notice that the second metric is actually weaker than
> first. In fact, if an algorithm achieves a constant lag bound, it must
> also achieve a constant bound for the second metric, but the reverse is
> not necessarily true. But in some settings, people have focused on the
> second metric and still consider an algorithm to be fair as long as the
> second metric is bounded by a constant.

Using these metrics it is possible to write benchmarks quantifying
fairness as a performance metric, provided weights for nice numbers.

Not so coincidentally, this also entails a test of whether nice numbers
are working as intended.


-- wli

P.S. Divide by the length of the time interval to rephrase in terms of
CPU bandwidth.
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