linux-kernel - Re: [RFC] Documentation about unaligned memory access

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Message-ID: <kjmpry1mgzs.fsf@pelargir.dolphinics.no>
Date:	Fri, 23 Nov 2007 10:46:31 +0100
From:	Arne Georg Gleditsch <argggh@...phinics.no>
To:	dean gaudet <dean@...tic.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Daniel Drake <dsd@...too.org>,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	kune@...ne-taler.de, johannes@...solutions.net
Subject: Re: [RFC] Documentation about unaligned memory access

dean gaudet <dean@...tic.org> writes:
> on AMD x86 pre-family 10h the boundary is 8 bytes, and on fam 10h it's 16 
> bytes.  the penalty is a mere 3 cycles if an access crosses the specified 
> boundary.

Worth noting though, is that atomic accesses that cross cache lines on
an Opteron system is going to lock down the Hypertransport fabric for
you during the operation -- which is obviously not so nice.

-- 
								Arne.
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