On Fri, Jan 30, 2009 at 07:07:34AM -0700, Michael H. Frese wrote: > Johnn Adams said "Facts are stubborn things," and there just aren't > enough of them in your example to determine whether bandwidth or latency > dominates communication time.
Mark asked for an example, not a research paper. And we were discussing something other than latency and bandwidth, because these 2 parameters aren't the only fundamental ones for a communications network. In the Berkeley "logp" model, for example, processor overhead and the "gap" betweeen messsages are fundamental parameters. The InfiniPath chip has a tiny "o" and a negative "g". As a result, it can send a lot more small messages than other interconnects, and this number rises as you add more cores to a system (!). Mark was wondering when that was important. Even logp doesn't describe an interconnect that well. It matters how efficient your interconnect is at dealing with multiple cores, and the number of nodes. As an example of that, MPI implementations for InfiniBand generally switch over to higher latency/higher overhead mechanisms as the number of nodes in a cluster rises, because the lowest latency mechanism at 2 nodes doesn't scale well. -- greg _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
