[Beowulf] Q: IB message rate & large core counts (per node) ?

richard.walsh at comcast.net richard.walsh at comcast.net
Thu Feb 25 18:27:25 PST 2010

Mark Hahn wrote: 

>Regardless of how tight the seastar per-hop latency is, 
>IB has 2.5x the per-hop fanout (2or 3 outgoing 9.6 GB links 
>versus 18 outgoing 4 GB/s links). higher radix means an 
>advantage that increases with size. 

Doesn't this assume worst case all-to-all type communication 
patterns. If you are just trading ghost cell data with your neighbors 
and you have placed your job smartly on the torus the fan out 
advantage mentioned is irrelevant. No? 

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