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Date: Mon, 23 Apr 2007 23:03:41 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>, Juliusz Chroboczek <jch@pps.jussieu.fr>,
       Con Kolivas <kernel@kolivas.org>, ck list <ck@vds.kolivas.org>,
       Bill Davidsen <davidsen@tmr.com>, Willy Tarreau <w@1wt.eu>,
       William Lee Irwin III <wli@holomorphy.com>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Mike Galbraith <efault@gmx.de>, Arjan van de Ven <arjan@infradead.org>,
       Peter Williams <pwil3058@bigpond.net.au>,
       Thomas Gleixner <tglx@linutronix.de>, caglar@pardus.org.tr,
       Gene Heskett <gene.heskett@gmail.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44
Message-ID: <20070423210341.GA7675@elte.hu>
References: <20070421160008.GA28783@elte.hu> <200704220959.34978.kernel@kolivas.org> <87647oblx5.fsf@pps.jussieu.fr> <alpine.LFD.0.98.0704221620310.9964@woody.linux-foundation.org> <20070423013429.GB25162@wotan.suse.de> <alpine.LFD.0.98.0704230844410.9964@woody.linux-foundation.org> <20070423191143.GA16849@elte.hu> <alpine.LFD.0.98.0704231227300.9964@woody.linux-foundation.org> <20070423203317.GA26668@elte.hu> <20070423204431.GA1240@elte.hu>
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* Ingo Molnar <mingo@elte.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