> > 3) Then, there's the switch. If it's a *switch* that sets up circuits, > > then it can be fairly inexpensive. If it's something that has to do packet > > buffering, it gets a lot more expensive. > > Switches (crossbars) don't scale for very many ports. Especially if you have > to
I'm a little mystified by this comment, since you can build arbitrary topologies using xbar primitives. for instance, quadrics fabrics are usually full-bisection fat-trees, and are composed of (iirc) 8x xbar switching chips. myrinet is <handwave>similar</handwave>. > do cut-through switching at those high speeds. It would be good if each NIC > would came with an integrated switch, with enough ports to wire at least a 3d > torus (where you route/switch messages via Bresenham). while I like multi-port designs, they do become huge investments in wire. > In regards to keeping the wires short, does this IBM trick of keeping all > wires equal-length work well on 3d lattices, and above? This would seem to > be a must for those coming (hopefully) Hypertransport motherboards with > connectors. afaikt, everyone now takes the approach of putting eq/deskew/etc logic on every pair or smallnumber of wires. HT certainly does that (including a clock per 8 data bits). I think pci-e is based on separate analog processing for each lane. _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
