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

[richard . brunner]

> -----Original Message-----
> From: Andi Kleen [mailto:ak@xxxxxxx] 
> Sent: Thursday, September 11, 2003 7:29 AM
> 
> On Thu, 11 Sep 2003 15:14:51 +0100
> Dave Jones <davej@xxxxxxxxxx> wrote:
> 
> > On Thu, Sep 11, 2003 at 04:01:08PM +0200, Andi Kleen wrote:
> > 
> >  > > 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.
 
] -Rich ...
] AMD Fellow

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