Modern switches need 100-150 ns per hop. There are some things that do not scale per hp such as traversing the PCIE link from socket to NIC and back. So, I see it as 1.2 to go to the router and back and 100 ns per hop.
Scott On Fri, Nov 9, 2012 at 11:17 AM, Vincent Diepeveen <[email protected]> wrote: > The latency estimate taking 5 hops seems a tad optimistic to me > except when i read the English wrong and they mean 1.7 microseconds a > hop making it for a 5 hop 5 * 1.7 = 8.5 microseconds in total. > > "Not every node is only one hop away, of course. On a fully > configured system, you are five hopes away maximum from any socket, > so there is some latency. But the delta is pretty small with > Dragonfly, with a minimum of about 1.2 microseconds for a short hop, > an average of 1.5 microseconds on average, and a maximum of 1.7 > microseconds for the five-hop jump, according to Bolding." > > On Nov 8, 2012, at 7:13 PM, Hearns, John wrote: > > > Well worth a read: > > > > > > > > http://www.theregister.co.uk/2012/11/08/ > > cray_cascade_xc30_supercomputer/ > > > > > > > > John Hearns | CFD Hardware Specialist | McLaren Racing Limited > > McLaren Technology Centre, Chertsey Road, Woking, Surrey GU21 4YH, UK > > > > > > T: +44 (0) 1483 262000 > > > > D: +44 (0) 1483 262352 > > > > F: +44 (0) 1483 261928 > > E: [email protected] > > > > W: www.mclaren.com > > > > > > > > The contents of this email are confidential and for the exclusive > > use of the intended recipient. If you receive this email in error > > you should not copy it, retransmit it, use it or disclose its > > contents but should return it to the sender immediately and delete > > your copy. > > > > _______________________________________________ > > Beowulf mailing list, [email protected] sponsored by Penguin > > Computing > > To change your subscription (digest mode or unsubscribe) visit > > http://www.beowulf.org/mailman/listinfo/beowulf > > _______________________________________________ > Beowulf mailing list, [email protected] sponsored by Penguin Computing > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf >
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