Re: [PATCH] x86_64/lib: improve the performance of memmove

[Andi Kleen]

> When the dest and the src do overlap and the memory area is large, memmove
> of
> x86_64 is very inefficient, and it led to bad performance, such as btrfs's
> file
> deletion performance. This patch improved the performance of memmove on
> x86_64
> by using __memcpy_bwd() instead of byte copy when doing large memory area
> copy
> (len > 64).


I still don't understand why you don't simply use a backwards
string copy (with std) ? That should be much simpler and
hopefully be as optimized for kernel copies on recent CPUs.

-Andi


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