[Fwd: Re: 32-port gigabit switch]
josip at nianet.org
Tue Mar 11 11:52:53 PST 2003
Mark Hahn wrote:
>>>>clusters. Remember on clusters latency is more important than
>>>Bzzt. Wrong. Dead Wrong. "It depends" is the correct answer. (Don't
>>>pass GO, don't collect $200).
> it does depend.
> but as generalizations go, bandwidth is easy; latency is hard.
Agreed. The "it depends" part can be seen in tests done at Dell:
The second paper
shows that on Gaussian elimination linear algebra problems "size-major"
process mapping on clusters of dual CPU nodes connected via Fast Ethernet
works better than "frequency-major" process mapping. Faster networks (Gigabit
Ethernet, Myrinet) reduced the advantage of "size-major" process mapping but
did not completely eliminate it. In other words, their Linpack test benefits
more from increased bandwidth than from decreased latency. This is just one
example; latency sensitive codes may lead to the opposite conclusion.
P.S. My own experience with NPB is similar to the first Dell paper:
Dr. Josip Loncaric, Research Fellow mailto:josip at nianet.org
National Institute of Aerospace http://research.nianet.org/~josip/
144 Research Drive mailto:j.loncaric at larc.nasa.gov
Hampton, VA 23666, USA Tel. +1-757-766-1395 Fax +1-757-766-1401
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