[Beowulf] Clos networking and myrinet

[Mikhail Kuzminsky]

In message from Greg Lindahl <lindahl at pathscale.com> (Wed, 8 Jun 2005 
11:02:40 -0700):
>On Tue, Jun 07, 2005 at 11:33:06AM -0400, Mack.Joseph at epamail.epa.gov 
>wrote:
>
>> >From other reading I find that 3 layer Clos networks
>> are blocking but that 5 (and above) layers are non-blocking.
>
>That blocking and non-blocking stuff is all a myth. Clos networks 
>have
>a special property if you are doing circuit switching, like is done 
>in
>the telecom market: Node A talks to Node B and only node B. With a
>Clos network, you have a dedicated path from A to B for every node on
>the network.
>
>In a Linux cluster, each node talks to multiple other nodes. So they
>always interfere with each other.
Sorry, why is it right ?
- for typical example, if I have a pair of nodes w/MPI_Send one 1st
and MPI_Recv on second ?

It looks for me that both Myrinet and Infiniband topologies
specially support "Clos-network configurations" ...

>
>> With large beowulfs, why is the diameter of the network
>> increased from 3 to 5 to 7...?
>
>Because the maximum number of nodes you can support with only 3 
>layers
>is limited by the size of the switch chips you're using. For the
>InfiniBand case, this size is 288 ports at 3 layers, because the
>building block is a 24-port crossbar switch chip.
>
>-- greg
>
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