Beowulf: A theorical approach
Robert G. Brown
rgb at phy.duke.edu
Thu Jun 22 13:12:27 PDT 2000
On Thu, 22 Jun 2000, [iso-8859-1] Jakob Østergaard wrote:
> On Thu, 22 Jun 2000, Greg Lindahl wrote:
> > > Just as a matter of curiosity -- Once upon a time some two or three
> > > years ago I suggested on the list that a development company consider
> > > building a network communications device that plugged into the second
> > > CPU slot of a dual CPU board.
> > It's hard to build something that plugs into an Intel-designed CPU bus.
> > Scali tried it and it didn't work so hot.
> At least on Intel hardware, SMP systems have cache coherency in the hardware,
> and that's _expensive_ wrt. inter-cpu communication. There's write snooping
> and all sorts of the strangest things happening. I cannot imagine how this
> could work in any way over a network with any reasonable performance. Even
> given infinite bandwidth, I guess the latency from ten meters of copper wiring
> would kill performance. (any sub-c interconnect would and tunneling is a few
> years away I guess ;)
Not arguing with the difficulty of doing the local engineering, but from
whence the remarks concerning copper and latency? It could be an
optical interconnect, or a three meter copper interconnect for all I
care. Even ten meters is only 33 nanoseconds at c which is a WHOLE lot
smaller than the other sources of latency in a normal network
interconnect. I thought signals propagated on copper at an appreciable
fraction of c... am I missing something here?
Never mind. I'll just go get the beer Greg suggested instead;-)
> > In 12 months, you'll be able to get either PCI-X machines or Infiniband
> > machines. PCI-X has split transactions, and Chuck Seitz, who knows more
> > about networking than all of us combined, says that PCI-X will get rid of
> > most of the PCI latency.
> > So, sit back, pop open a cold one, and wait.
> I'm skeptical, but I'll take your advice here :)
Robert G. Brown http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567 Fax: 919-660-2525 email:rgb at phy.duke.edu
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