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

[Pavel Machek]

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?]
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