Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata

Pavel Machek
2003-09-13T16:54:42Z

Hi!

> > > > > What's wrong with the current status quo that just says
> > > > > "Athlon prefetch is broken"?
> > > > It doesn't fix user space for once.
> > >
> > > And for another, it cripples the earlier athlons which
> > > don't have this
> > > errata. Andi's fix at least makes prefetch work again on
> > > those boxes.
> > > It's also arguable that prefetch() helps the older K7's
> > > more than the
> > > affected ones.
> >
> > All Athlons have this Errata. I can trigger it on an old
> > 900Mhz pre XP Athlon too. You just have to use 3dnow prefetch
> > instead of SSE prefetch.
> >
> > BTW the older Athlons currently don't use prefetch because
> > the alternative
> > patcher does not handle 3dnow style prefetch.
> >
>
> Avoiding prefetch for all Athlons and earlier Opterons/Athlon64
> even in the kernel can really tank performance. And as Andi says
> it still doesn't solve user mode from hitting the errata.

How much speedups can be expected from prefetch? 5%?
Pavel
--
When do you have a heart between your knees?
[Johanka's followup: and *two* hearts?]