AMD Opteron memory bandwidth (was Re: CPUs for a Beowulf)
hahn at physics.mcmaster.ca
Tue Sep 9 09:27:46 EDT 2003
> > If you could connect those HyperTransport channels into a scalable mesh
> > then this sounds a lot like the good old Cray T3E design. Drool... It's
> > too bad that Red Storm won't be taking that route. The T3E was so nice.
> The article I quoted from Digit Life floats the idea that AMD may be able
> to make for Cray an Opteron with 4 Hypertransports, making a 3D mesh
> possible. Is this just supposition?
it would be astonishing if AMD hadn't prototyped this already.
one sticking point is that the current architecture is based on broadcast
for managing coherence. a big-scalable approach would need to be
directory-based, perhaps assisted by the OS. I dimly recall that the
current packet format has just three bits for node ID. I have an even
more dim recollection that current HT is limited to 20cm; perhaps that
would be enough for a non-torus mesh.
but, as Dell points out, the market for such things is rather small.
regards, mark hahn.
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