linux-kernel - Re: kernel + gcc 4.1 = several problems

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Message-ID: <Pine.LNX.4.64.0701030805530.4473@woody.osdl.org>
Date:	Wed, 3 Jan 2007 08:06:29 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Alan <alan@...rguk.ukuu.org.uk>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Grzegorz Kulewski <kangur@...com.net>,
	Mikael Pettersson <mikpe@...uu.se>, s0348365@....ed.ac.uk,
	76306.1226@...puserve.com, akpm@...l.org, bunk@...sta.de,
	greg@...ah.com, linux-kernel@...r.kernel.org,
	yanmin_zhang@...ux.intel.com
Subject: Re: kernel + gcc 4.1 = several problems



On Wed, 3 Jan 2007, Alan wrote:
>
> > cmov is effectively the same cost as a compare and jump, in both cases
> > the cpu needs to do a prediction, and on a mispredict, restart.
> 
> On a P4 it appears to be slower than compare/jump in most cases

On just about EVERYTHING it's slower than compare/jump. See my other post 
on why, together with a (largely untested) test app.

		Linus
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