On Thu, Aug 03, 2006 at 11:19:44AM +0200, Joachim Worringen wrote: > From the numbers published by Pathscale, it seems that the simple MPI > latency of Infinipath is about the same whether you go via PCIe or HTX. > The application perfomance might be different, though.
No, our published number is 1.29 usec for HTX and 1.6-2.0 usec for PCI Express. It's the message rate that's about the same. BTW there are more HTX motherboards appearing: the 3 IBM rack-mount Opteron servers announced this Tuesday all have HTX slots: http://www-03.ibm.com/systems/x/announcements.html In most HTX motherboards, a riser is used to bring out either HTX or PCI Express, so you don't have to sacrifice anything. That's why IBM can put HTX in _all_ of their boxes even if most won't need it, because it doesn't take anything away except a little board space. The existing SuperMicro boards work like this, too. Vincent wrote: > Only quadrics is clear about its switch latency (probably > competitors have a worse one). It's 50 us for 1 card. We have clearly stated that the Mellanox switch is around 200 usec per hop. Myricom's number is also well known. Mark Hahn wrote: > I intuit (totally without rigor!) that fatter nodes do increase bandwidth > needs, but don't necessarily change the latency picture. Fatter nodes mean more cpus are simultaneously trying to send out messages, so yes, there is an effect, but it's not quite latency: it's that message rate thing that I keep on talking about. http://www.pathscale.com/performance/InfiniPath/mpi_multibw/mpi_multibw.html Poor scaling as nodes get faster are the dirty little secret of our community; our standard microbenchmarks don't explore this, but today's typical nodes have 4 or more cores. -- greg _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
