linux-kernel - Re: [PATCH] tcp_cubic: faster cube root

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Message-ID: <20070307121246.GA7728@one.firstfloor.org>
Date:	Wed, 7 Mar 2007 13:12:46 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	David Miller <davem@...emloft.net>
Cc:	shemminger@...ux-foundation.org, rkuhn@....physik.tu-muenchen.de,
	andi@...stfloor.org, dada1@...mosbay.com, jengelh@...ux01.gwdg.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] tcp_cubic: faster cube root

On Tue, Mar 06, 2007 at 08:20:52PM -0800, David Miller wrote:
> From: Stephen Hemminger <shemminger@...ux-foundation.org>
> Date: Tue, 6 Mar 2007 14:47:06 -0800
> 
> > The Newton-Raphson method is quadratically convergent so
> > only a small fixed number of steps are necessary.
> > Therefore it is faster to unroll the loop. Since div64_64 is no longer
> > inline it won't cause code explosion.
> > 
> > Also fixes a bug that can occur if x^2 was bigger than 32 bits.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...ux-foundation.org>
> 
> Applied, thanks Stephen.

Well that still needs the ugly div64_64 function. At least my goal was to 
eliminate that, not make it faster (I don't see any evidence this function 
is particularly performance critical). You prefer to keep div64_64? 

-Andi
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