On Thu, Nov 13, 2008 at 08:54:35PM +0300, Mikhail Kuzminsky wrote:
> I read somewhere that exact evidence of "non-blocking" was performed for
> Clos networks with >= 3 levels. But most popular Infiniband fat trees has
> only 2 levels.
Two is three: if you have
spine spine
| \/ |
leaf leaf
/ \ / \
node node node node
that's a 3-level network in Clos-speak, because the image you should really
imagine is
node node
\ /
leaf
/ \
spine spine
\ /
leaf
/ \
node node
Or, to think about it another way, you have to go through 3 switches
max to get from a node to another. This is also sometimes called the
network diameter.
> (Yes, I know that "non-blocking" for Clos network isn't "absolute" :-))
So useless that it doesn't even help to mention "non-blocking", unless each node
only talks to exactly 1 other node. In which case I won't complain if you
mention
the standard "latency" and "bandwidth" benchmarks ;-)
-- greg
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