Benjamin Herrenschmidt [off-list ref] wrote on 14/01/2010 10:43:44:

On Thu, 2010-01-14 at 10:12 +0100, Joakim Tjernlund wrote:

quoted

quoted

No, that was on purpose. If an arch doesn't have efficient unaligned
accesses, then they should not use the optimization since it will

result

quoted

in a lot of unaligned accesses :-) In which case they are better off
falling back to the old byte-by-byte method.

Not quite, it is only 1 of 4 accesses that uses unaligned and
that accesses is only unaligned 50% in average, it might still
be faster. We will never know now.

Why ? If you think it's a win, then it's easy to make a patch to turn
it to __KERNEL__ and ask some people from ARM and MIPS or even sparc
land for example to give it a spin. If it's indeed a win, then submit it
to Linus and/or Andrew and there's no reason for it not to go in.

I simply took a more conservative approach for post -rc4

It would probably be a good idea to redefine UP_UNALIGNED macro to
do 2 byte accesses in the non CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS case.

I don't think I will revisit this any time soon so I figured I should
mention it in case someone else wants to try it.

         Jocke