[Beowulf] Win64 Clusters!!!!!!!!!!!!
hahn at mcmaster.ca
Wed Apr 11 13:18:18 PDT 2007
> performance boost when going to 64 bit in most situations. Core 2 chips
> suffer a small penalty when going 64 bit. I suspect this is due to the
Core2 has some micro-optimizations which are only enabled for 32b mode,
which is an interesting choice. AMD tends to be biased towards HPC
or at least serverish stuff, which is 64b-oriented...
> cache hit rate suffering which, with a traditional north bridge, would
> have proportionally more effect.
I can't think of negative effects of x86_64 other than possible
higher memory overhead for apps that use lots of pointers.
compilers are a typical example, but perhaps some sparse matrix stuff, too?
code density in x86_64 mode is not much different in mcmodel=small
(for instance, it's not the case that every offset in branch and memory
reference instructions become giant...)
it'll be most interesting to see how AMD has optimized Barcelona...
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