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

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Message-ID: <20070424073103.GA29054@elte.hu>
Date:	Tue, 24 Apr 2007 09:31:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rogan Dawes <lists@...es.za.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Gene Heskett <gene.heskett@...il.com>,
	Juliusz Chroboczek <jch@....jussieu.fr>,
	Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org,
	Peter Williams <pwil3058@...pond.net.au>,
	ck list <ck@....kolivas.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Lee Irwin III <wli@...omorphy.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bill Davidsen <davidsen@....com>, Willy Tarreau <w@....eu>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44


* Rogan Dawes <lists@...es.za.net> wrote:

> >        if (p_to && p->wait_runtime > 0) {
> >                p->wait_runtime >>= 1;
> >                p_to->wait_runtime += p->wait_runtime;
> >        }
> >
> >the above is the basic expression of: "charge a positive bank balance". 
> >
> 
> [..]
> 
> > [note, due to the nanoseconds unit there's no rounding loss to worry 
> > about.]
> 
> Surely if you divide 5 nanoseconds by 2, you'll get a rounding loss?

yes. But not that we'll only truly have to worry about that when we'll 
have context-switching performance in that range - currently it's at 
least 2-3 orders of magnitude above that. Microseconds seemed to me to 
be too coarse already, that's why i picked nanoseconds and 64-bit 
arithmetics for CFS.

	Ingo
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