linux-kernel - Re: [PATCH] x86-64: make pda's cpunumber and nodenumber unsigned

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Message-ID: <20071217132619.GB1870@elte.hu>
Date:	Mon, 17 Dec 2007 14:26:19 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86-64: make pda's cpunumber and nodenumber unsigned


* Jan Beulich <jbeulich@...ell.com> wrote:

> This generally allows better code to be generated, since the zero- 
> extension during 32-bit operations comes for free (needed when the 
> result is used as array index or similar), whereas sign extension must 
> be done explicitly and frequently requires a one byte larger 
> instruction due to the necessary rex64 prefix.

good catch! Applied your patch to x86.git - queued it up for v2.6.25. I 
bet there are tons of other instances where we use signed instead of 
unsigned and get worse code generation.

	Ingo
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