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

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Message-Id: <476689AF.76E4.0078.0@novell.com>
Date:	Mon, 17 Dec 2007 13:37:35 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	<tglx@...utronix.de>, "Andrew Morton" <akpm@...ux-foundation.org>,
	<mingo@...hat.com>, <linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86-64: make pda's cpunumber and nodenumber
	unsigned

>>> Ingo Molnar <mingo@...e.hu> 17.12.07 14:26 >>>
>
>* 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.

Yes, definitely. This patch was kind of a testing one whether this is a
welcome change. As it appears to be, I'll probably produce more as I
run into respective cases.

Jan

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