[Beowulf] How to configure a cluster network

Lawrence Stewart larry.stewart at sicortex.com
Fri Jul 25 11:50:06 EDT 2008


Mark Hahn wrote:
>> It is my sacred duty to rescue hypercube topology. Cool Preceeds
>> Coolant :-)
>
> I agree HC's are cool, but I think they fit only a narrow ecosystem:
> where you don't mind lots of potentially long wires, since higher
> dimensional
> fabrics are kind of messy in our low-dimensional universe.  also, HC's
> assume intelligent routing on the vertices, so you've got to make the
> routing overhead low relative to the physical hop latency.
>
> it does seem like there is some convergence to using rings onchip,
> fully connected graphs within a node and fat trees inter-node.
> one unifying factor is that these are all point-to-point topologies...
Hypercubes give log diameter, which is good, but when you grow the machine
you have to add more ports to each node, which is not so good once you run
out of pins.

Other topologies, such as Kautz and deBruijn graphs, give log diameter
as well,
but with a fixed number of ports per node, so you can put the node on
one chip
and still build systems of greater or lesser size without having to respin.

You can route arbitrary size Kautz graphs on a
fixed number of layers, so when these somewhat wacky topologies
go on chip you can still route it on N metal layers.

The point about long wires is well taken, but I think it is the price of
low diameter.

-- 
-Larry / Sector IX

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