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

Ingo Molnar
2009-11-13T07:34:17Z

* Pavel Machek <pavel@ucw.cz> wrote:

> > Ling, if you are interested, could you send a user-space test-app to
> > this thread that everyone could just compile and run on various older
> > boxes, to gather a performance profile of hand-coded versus string ops
> > performance?
> >
> > ( And i think we can make a judgement based on cache-hot performance
> > alone - if then the strings ops will perform comparatively better in
> > cache-cold scenarios, so the cache-hot numbers would be a conservative
> > estimate. )
>
> Ugh, really? I'd expect cache-cold performance to be not helped at all
> (memory bandwidth limit) and you'll get slow down from additional
> i-cache misses...

That's my point - the new code is shorter, which will run comparatively
faster in a cache-cold environment.

Ingo