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

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Message-ID: <20070423210341.GA7675@elte.hu>
Date:	Mon, 23 Apr 2007 23:03:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>,
	William Lee Irwin III <wli@...omorphy.com>,
	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


* Ingo Molnar <mingo@...e.hu> wrote:

> sorry, i was a bit imprecise here. There is a case where CFS can give 
> out a 'loan' to tasks. The scheduler tick has a low resolution, so it 
> is fundamentally inevitable [*] that tasks will run a bit more than 
> they should, and at a heavy context-switching rates these errors can 
> add up significantly. Furthermore, we want to batch up workloads.
> 
> So CFS has a "no loans larger than sched_granularity_ns" policy (which 
> defaults to 5msec), and it captures these sub-granularity 'loans' with 
> nanosec accounting. This too is a very sane economic policy and is 
> anti-infationary :-)

at which point i guess i should rename CFS to 'EFS' (the Economic Fair 
Scheduler)? =B-)

	Ingo
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