----- Forwarded message from Patrick Geoffray <[EMAIL PROTECTED]> -----
From: Patrick Geoffray <[EMAIL PROTECTED]> Date: Fri, 12 Nov 2004 17:51:48 -0500 To: Joachim Worringen <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED] Subject: Re: [Beowulf] torus versus (fat) tree topologies Organization: Myricom User-Agent: Mozilla Thunderbird 0.8 (X11/20040921) Hi Joachim, It was good to see you at SC. Joachim Worringen wrote: >Yes, a feature of the NIC, plus: the torus doesn't affect the latency >significantly. In fact, the cost of a hop in an SCI-based torus, like an >other reasonable modern torus, is only a low number of nanoseconds (I'd >have to look it up right now for an exact number which I can not do from >here; I think there's also such a number in a recent publication on >BlueGene). A hop in a router node has about the same delay (as it is has >a similar task). Going trough a crossbar cost about 100-150ns these days. I would expect the cost of one hop to be roughly the same in a torus. Now, the interesting number is the number of hops for a given number of nodes. With a 32-ports crossbar, you have one hop for 32 nodes. For 1280 nodes, you can build a Clos topology of diameter 5, thus 5 hops. With a 3D Torus, you route on a hypercube, so you have one hop for 8 nodes. I let the pleasure to compute the number of hops for a 1280 nodes 3D torus to a volunteer :-) So the fabric overhead will depend on the size of the machine, as always. Another consideration is the cabling. With 3D torus, you have 6 links going to each node. If they are on a backplane like BlueGene, that's fine. However, if those are short fat copper cables, you are in for a good time... Patrick -- Patrick Geoffray Myricom, Inc. http://www.myri.com _______________________________________________ Beowulf mailing list, [EMAIL PROTECTED] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org";>leitl</a> ______________________________________________________________ ICBM: 48.07078, 11.61144 http://www.leitl.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE http://moleculardevices.org http://nanomachines.net ------- To unsubscribe, change your address, or temporarily deactivate your subscription, please go to http://v2.listbox.com/member/[EMAIL PROTECTED]
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