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

[Nick Piggin <piggin@cyberone.com.au>]

Andrew Morton wrote:

>Nick Piggin <piggin@cyberone.com.au> 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.