linux-kernel - Re: [ANNOUNCE][RFC] PlugSched-6.4 for 2.6.18-rc2

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Message-Id: <200607261128.k6QBSJ4o020737@turing-police.cc.vt.edu>
Date:	Wed, 26 Jul 2006 07:28:19 -0400
From:	Valdis.Kletnieks@...edu
To:	Al Boldi <a1426z@...ab.com>
Cc:	Peter Williams <pwil3058@...pond.net.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [ANNOUNCE][RFC] PlugSched-6.4 for 2.6.18-rc2

On Wed, 26 Jul 2006 07:45:33 +0300, Al Boldi said:
> Valdis.Kletnieks@...edu wrote:

> > On an SMP system, you can have one CPU doing one class of scheduling (long
> > timeslice for computational, for example), while another CPU is dedicated
> > to doing RT scheduling, and so on.  It's not clear to me that "different
> > classes per CPU" makes any real sense on a UP....
> 
> Conceptually there should be no difference between UP and MP.
> 
> Think HyperThreading.

Which is why a UP kernel can schedule on both sides of an HT core.

Yeah, I got it now. ;)

An HT core still *has* "the other instruction stream" it can schedule
differetly.  You can't say "We'll schedule this one this way and that other
one that way" when there *is* no "that other one".

(And if you look at the current code, you'll realize that HT is conceptually
different from both UP *and* MP - go look at the places where the *current*
scheduler is HT-aware, and how that was a big win over when it thought each
HT was a fully capable MP......)

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