[U-Boot] [PATCH] uboot optimize memmove

[Wolfgang Denk]

Dear Andy Green,

In message <20130726065323.27333.82421.stgit at localhost.localdomain> you wrote:
> While studying the reason why kernel copy from NOR was so slow on our platform,
> I realized U-Boot is pulling it from 32-bit NOR in 8-bit chunks needlessly.
> 
> bootm uses memmove() and that just takes the approach by default to move u8s
> around.
> 
> This optimization prefers memcpy() implementation (done mostly in 32-bit reads
> and writes) if there's no overlap in source and dest, resulting in a huge
> speedup on our platform (480ms copy from 32-bit NOR ---> 140ms)

Sorry, but I dislike your patch.

Instead of making assumptions on the performance of memcpy() and
adding the overhead of an additional function call (which can be
expensive especially for short copy operations) it would make more
sense to pull the "copy a word at a time" code from memcpy() into
memmove(), too.

On the other hand - if you really care about performance, then why do
you not make sure that you provide optimized implementations for such
functions and consequently #define __HAVE_ARCH_MEMMOVE (and
__HAVE_ARCH_MEMCPY) ?

Best regards,

Wolfgang Denk

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