Re: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers

[Nick Piggin]

Andrew Morton wrote:

> Nick Piggin <piggin@xxxxxxxxxxxxxxx> wrote:
>
> > What is intriguing to me is the "Its only a 2% slowdown of the page
> > fault for every cpu other than K[78] for this single workaround. There
> > is no point to conditional compilation" attitude some people have.
> > Of course, its only 2% on a pagefault, not anywhere near 2% of kernel
> > performance as a whole, so maybe that is justified.
>
> Absolutely.  But it's a bit of a pain finding a config option which says
> "this CPU might need the fixup".

Right. It obviously can't be done using the current system.

> > Just repeating though, that is a seperate issue and I think Andi's patch
> > is needed.
>
> It is unquestionably needed - the kernel _has_ to perform the fixup for this
> CPU erratum.
>
>
> But I would like to see some evidence that prefetch ever provides any
> performance gain in-kernel.  I spent some time fiddling a while back and
> was unable to demonstrate any difference.

OK. I just liked this patch because apparently it fixes userspace as
well. Disabling prefetch for the kernel doesn't.


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