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

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Message-ID: <4626713B.1040206@nortel.com>
Date:	Wed, 18 Apr 2007 13:27:55 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Mark Glines <mark@...nes.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, Nick Piggin <npiggin@...e.de>,
	Bill Huey <billh@...ppy.monkey.org>,
	Mike Galbraith <efault@....de>,
	Peter Williams <pwil3058@...pond.net.au>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org, ck list <ck@....kolivas.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [ck] Re: [Announce] [patch] Modular Scheduler Core and Completely
 Fair Scheduler [CFS]

Mark Glines wrote:

> One minor question: is it even possible to be completely fair on SMP?
> For instance, if you have a 2-way SMP box running 3 applications, one of
> which has 2 threads, will the threaded app have an advantage here?  (The
> current system seems to try to keep each thread on a specific CPU, to
> reduce cache thrashing, which means threads and processes alike each
> get 50% of the CPU.)

I think the ideal in this case would be to have both threads on one cpu, 
with the other app on the other cpu.  This gives inter-process fairness 
while minimizing the amount of task migration required.

More interesting is the case of three processes on a 2-cpu system.  Do 
we constantly migrate one of them back and forth to ensure that each of 
them gets 66% of a cpu?

Chris
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