Re: Big git diff speedup by avoiding x86 "fast string" memcmp

[Nick Piggin]

On Wed, Dec 15, 2010 at 12:38:40PM +0800, Américo Wang wrote:
> On Mon, Dec 13, 2010 at 07:25:05PM +1100, Nick Piggin wrote:
> >On Mon, Dec 13, 2010 at 6:29 PM, J. R. Okajima <hooanon05@xxxxxxxxxxx> wrote:
> >> But is the "rep cmp has quite a long latency" issue generic for all x86
> >> architecture, or Westmere system specific?
> >
> >I don't believe it is Westmere specific. Intel and AMD have
> >been improving these instructions in the past few years, so
> >Westmere is probably as good or better than any.
> >
> >That said, rep cmp may not be as heavily optimized as the
> >set and copy string instructions.
> >
> >In short, I think the change should be suitable for all x86 CPUs,
> >but I would like to hear more opinions or see numbers for other
> >cores.
> >
> 
> How about other arch? If this is only for x86, shouldn't it be
> protected by CONFIG_X86?

That's what I would like to know, but I suspect that for very short
strings we are dealing with, the custom loop will be fine for
everybody.

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