Messages in this thread | | | Date | Wed, 17 Sep 2003 07:26:50 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers |
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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? @)
It is not 2%, but <1% [~0.6% to be exact]
(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.
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.
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