linux-kernel - Re: Non atomic unaligned writes

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Message-ID: <20070820102306.GG16680@bingen.suse.de>
Date:	Mon, 20 Aug 2007 12:23:07 +0200
From:	Andi Kleen <ak@...e.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Andi Kleen <ak@...e.de>, patches@...-64.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Zachary Amsden <zach@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	"S. P. Prasanna" <prasanna@...ibm.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: Non atomic unaligned writes

> Intel486???, Pentium??, or P6 family processors. The P6 family processors
> provide bus control signals that permit external memory subsystems to
> make split accesses atomic; however, nonaligned data accesses will

Normally in standard SMP systems between CPUs they are atomic AFAIK 
(modulo bugs) 

You're right -- i'm not sure about P5 SMP.

> seriously impact the performance of the processor and should be avoided
> where possible.

But they're also slow yes.

-Andi
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