linux-kernel - Re: x86 - cpu_relax

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Message-ID: <4B701292.3030108@gmail.com>
Date:	Mon, 08 Feb 2010 14:33:06 +0100
From:	Artur Skawina <art.08.09@...il.com>
To:	Michael Breuer <mbreuer@...jas.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: x86 - cpu_relax - why nop vs. pause?

Michael Breuer wrote:
> Just to move away from this... totally perplexed, I retested a bit.
> Seems something else had gone wrong causing me to try 'rep;pause' vs.
> 'pause'. The resulting opcode is f3 f3 90, as noted above.
> 
> I do see what seems to be a small but noticeable performance improvement
> - no idea if there's a downside, and also no idea what f3 f3 90 does vs.
> f3 90. Might be something interesting, or maybe not.

Alignment? IOW what happens if you use eg "nop; rep; nop;" or "rep; nop; nop;"?
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