Messages in this thread | | | Date | Wed, 17 Sep 2003 15:44:08 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers |
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Andi Kleen wrote:
>On Wed, 17 Sep 2003 14:53:40 +1000 >Nick Piggin <piggin@cyberone.com.au> wrote: > > >>The conditional compilation thing is a seperate issue. This patch may >>have just broken a few camels' backs. >> >>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 >> > >Erm. It helps to get your numbers right first when arguing. Why did I waste the >time on benchmarking and collecting data when people afterwards still argue with >bogus numbers? @) >
I was using your numbers.
> >It is not 2%, but <1% [~0.6% to be exact] >
100 * (3.7268 - 3.65945) / 3.65945 = 1.8 (am I wrong?)
> >(probably lower the statistical error for the test, LMBench results vary more >than that on multiple runs) > >Then it is not for all page faults, but only for a very narrow special >case - a page fault that is not handled, but causes a signal. These are >not very common. Arguably there are some applications that use this >stuff (like generational garbage collectors), but these are not exactly >common. >
I missed that, sorry.
> >In summary, it causes 0.6% slowdown in an quite obscure use case. > >That's small enough that it is best to just always enable it, because >the cost of processing any support request when people forget to enable >etc. is much greater. >
I agree that with the current cpu selection arrangements it has to be always enabled. I'm talking about Adrian's patch though.
I wasn't really arguing about it based on it causing a big slowdown. I just don't agree with your opinion (which you're very entitled to) on the matter.
I think that messing up your config options is a user error anyway. And obviously a big reason for config options is so you don't have to compile everything, are we really going to try catering for people who make the wrong choices?
Aside, I think Adrian's patch makes cpu selection simpler for users, and if it was combined with a warning for booting a non selected cpu I can't see it being any more of a support problem.
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