Messages in this thread | | | Subject | Re: [RFC] Documentation about unaligned memory access | From | Andi Kleen <> | Date | Fri, 23 Nov 2007 03:07:05 +0100 |
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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.
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