From: Andi Kleen <andi@firstfloor.org>
To: Robert Hancock <hancockr@shaw.ca>
Cc: Daniel Drake <dsd@gentoo.org>,
linux-kernel@vger.kernel.org, davem@davemloft.net
Subject: Re: [RFC] Documentation about unaligned memory access
Date: Fri, 23 Nov 2007 03:07:05 +0100 [thread overview]
Message-ID: <p73k5o9iuk6.fsf@bingen.suse.de> (raw)
In-Reply-To: <47462BBC.2000206@shaw.ca> (Robert Hancock's message of "Thu\, 22 Nov 2007 19\:24\:12 -0600")
Robert Hancock <hancockr@shaw.ca> writes:
>
> Also, x86 doesn't prohibit unaligned accesses,
That depends, e.g. for SSE2 they can be forbidden.
> but I believe they have
> a significant performance cost and are best avoided where possible.
On Opteron the typical cost of a misaligned access is a single cycle
and some possible penalty to load-store forwarding.
On Intel it is a bit worse, but not all that much. Unless you do
a lot of accesses of it in a loop it's not really worth something
caring about too much.
-Andi
next prev parent reply other threads:[~2007-11-23 2:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <fa.U+CIv4JClOmn6KppLkEOSk7RW0Y@ifi.uio.no>
2007-11-23 1:24 ` [RFC] Documentation about unaligned memory access Robert Hancock
2007-11-23 2:07 ` Andi Kleen [this message]
2007-11-23 0:15 Daniel Drake
2007-11-23 0:27 ` Avuton Olrich
2007-11-23 1:29 ` Alan Cox
2007-11-23 3:04 ` Kyle Moffett
2007-11-23 6:18 ` dean gaudet
2007-11-23 9:46 ` Arne Georg Gleditsch
2007-11-26 14:50 ` dean gaudet
2007-11-23 1:29 ` David Miller
2007-11-23 10:06 ` Jan Engelhardt
2007-11-23 11:43 ` Heikki Orsila
2007-11-25 11:16 ` Geert Uytterhoeven
2007-11-25 11:24 ` Heikki Orsila
2007-11-26 0:48 ` Alan Cox
2007-11-26 17:12 ` Ben Dooks
2007-11-27 7:51 ` Kumar Gala
2007-11-23 22:02 ` Vadim Lobanov
2007-11-23 22:52 ` Dmitri Vorobiev
2007-11-24 13:34 ` Pierre Ossman
2007-11-24 15:50 ` Luciano Rocha
2007-11-24 16:19 ` Pierre Ossman
2007-11-24 17:22 ` Luciano Rocha
2007-11-24 17:35 ` Pierre Ossman
2007-11-24 18:28 ` Luciano Rocha
2007-11-24 17:53 ` Haavard Skinnemoen
2007-11-25 8:27 ` Denys Vlasenko
2007-11-25 14:13 ` Olaf Titz
2007-11-26 9:14 ` DM
2007-11-26 14:47 ` Johannes Berg
2007-11-27 0:40 ` Arnaldo Carvalho de Melo
2007-11-26 14:51 ` Johannes Berg
2007-11-30 8:18 ` Jörn Engel
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