Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by fast string.

H. Peter Anvin
2009-11-06T19:26:14Z

On 11/06/2009 09:07 AM, H. Peter Anvin wrote:
>
> Where did the 1024 byte threshold come from? It seems a bit high to me,
> and is at the very best a CPU-specific tuning factor.
>
> Andi is of course correct that older CPUs might suffer (sadly enough),
> which is why we'd at the very least need some idea of what the
> performance impact on those older CPUs would look like -- at that point
> we can make a decision to just unconditionally do the rep movs or
> consider some system where we point at different implementations for
> different processors -- memcpy is probably one of the very few
> operations for which something like that would make sense.
>

To be expicit: Ling, would you be willing to run some benchmarks across
processors to see how this performs on non-Nehalem CPUs?

-hpa