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

[Andrew Morton]

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".

>  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.

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