[Beowulf] Network considerations for new generation cheap beowulfcluster

Mark Hahn hahn at mcmaster.ca
Mon May 21 21:38:13 PDT 2007

>>> It is not just HPC applications that are demanding low latency networks.
>> what applications are you thinking of?  the only I can think of would be 
>> lock/metadata traffic for very large parallel clustered DB/filesystem,
>> and even there the argument is weak.
> I'm thinking of applications like on-line video games (first-person shooters, 
> real-time strategy, massively multi-player role-playing, etc. benefit from 
> lower latencies) and automatic electronic stock trading to name a few.

humans are deadly slow, and tend to be separated by geograpic latency.
the first hop on my cable connection is is 7 ms (perhaps not excellent), 
and all latency aspects of human perception are in that range.  I have 
a hard time seeing how games would notice the difference between 60
and 30 us (readily achievable by Gb), let alone even detect 1-4 us latency
of current HPC interconnect...

unless you're suggesting that games use collectives akin to MPI 

I'm guessing that online auto-trading has "think time" that dominates 
1-100 us network latency.  again, geography and network topology would 
probably make more difference than shaving 30 us down to 10...

regards, mark hahn.

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