Robert G. Brown wrote:
On Tue, 22 May 2007, Larry Stewart wrote:
What would the advantages of a diamond lattice be? In terms of
bisection and diameter?
Ease of wiring?
Four ports per system, probably, in a 3d lattice. 3d is good because
the volume (number of hosts) scales like the maximum number of hops
between hosts cubed.
Ah. I see that. I looked at the diamond lattice picture in
http://phycomp.technion.ac.il/~nika/diamond_structure.html
and it did make my head twinge.
With Kautz or deBruijn graphs, you get an exponential number of nodes,
for node degree
k >= 2, and diameter (hopcount D) you get O(k**D) nodes. However, you
don't get any
obvious mapping of 2D or 3D problems to the graph. You could do this
with two
NICs per node, if you can send the transmit data and the receive data to
different places.
Of course even on BlueGene/L they use simulated annealing to map the
problem to the
machine, because the obvious mapping is often not the best one.
See "Optimizing Task Layout on the BlueGene/L Supercomputer" in IBM JSRD
March 2005.
-Larry
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