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

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Message-ID: <20070417071126.GG1057@wotan.suse.de>
Date:	Tue, 17 Apr 2007 09:11:26 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	William Lee Irwin III <wli@...omorphy.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Mike Galbraith <efault@....de>,
	Con Kolivas <kernel@...ivas.org>, Ingo Molnar <mingo@...e.hu>,
	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 Mon, Apr 16, 2007 at 11:50:03PM -0700, Davide Libenzi wrote:
> On Tue, 17 Apr 2007, Nick Piggin wrote:
> 
> > > All things are not equal; they all have different properties. I like
> > 
> > Exactly. So we have to explore those properties and evaluate performance
> > (in all meanings of the word). That's only logical.
> 
> I had a quick look at Ingo's code yesterday. Ingo is always smart to 
> prepare a main dish (feature) with a nice sider (code cleanup) to Linus ;)
> And even this code does that pretty nicely. The deadline designs looks 
> good, although I think the final "key" calculation code will end up quite 
> different from what it looks now.
> I would suggest to thoroughly test all your alternatives before deciding. 
> Some code and design may look very good and small at the beginning, but 
> when you start patching it to cover all the dark spots, you effectively 
> end up with another thing (in both design and code footprint).
> About O(1), I never thought it was a must (besides a good marketing 
> material), and O(log(N)) *may* be just fine (to be verified, of course).

To be clear, I'm not saying O(logN) itself is a big problem. Type

  plot [10:100] x with lines, log(x) with lines, 1 with lines

into gnuplot. I was just trying to point out that we need to evalute
things. Considering how long we've had this scheduler with its known
deficiencies, let's pick a new one wisely.
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