linux-kernel - Re: [patch 13/17] Immediate Values

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Message-ID: <47FD6399.6030302@zytor.com>
Date:	Wed, 09 Apr 2008 17:47:21 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Adrian Bunk <bunk@...sta.de>,
	Alexey Dobriyan <adobriyan@...il.com>, akpm@...l.org
Subject: Re: [patch 13/17] Immediate Values - x86 Optimization

Mathieu Desnoyers wrote:
> 
> Ok. Sorry, it's been a few months since we looked at this. So the =q
> opcode lets the compiler choose instructions with or without REX prefix.
> We can allow this because 
> 
> - We don't need the opcode length in the stop_machine_run() version
> - we support variable length opcode in the nmi-safe version
> 
> Am I remembering correctly now ?
> 

Yes.  Both =r and =q allow REX opcodes.

	-hpa
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