[Beowulf] Max flops to watts hardware for a cluster

Jim Lux james.p.lux at jpl.nasa.gov
Tue Feb 17 00:34:30 EST 2004

> This document describes how to encapsulate Internet Protocol
> version 4 and version 6 packets can be encapsulated in
> Consultative Committee for Space Data Systems (CCSDS) Space
> Data Link Protocols.
> That's going to be one hell of a round trip time for pings..
> <ObCluster>
> What about distributed processing between spacecraft ?   OK, maybe
> interplanetary would be a bit much, but what about lander(s) and
orbiter(s) ?
> </ObCluster>

Such ideas are being contemplated, and not only by me.  There are
distributed computing/ cooperative robotics sorts of things, and also
"formation flying" sorts of things, not to mention "sensor webs".

 Probably the biggest problem is not a technology one but a philosophical
one.  Spacecraft and mission design is exceedingly conservative, and you'd
have to show that it would enable something that's needed, that can't be
done by conventional approaches. It's sufficiently unusual that it doesn't
fit well with the usual analysis models for spacecraft; which tend to push
towards "one big X" supplied by power from "one big Y" using "one big Z" to
talk to home, etc.  The costing spreadsheets used in speculative mission
planning don't have cells for "number of processors in cluster" and "power
per node"   You need a fairly straightforward model that says, in effect,
you can process "x" amount of data with "y" mass and "z" watts/joules. That
model must be backed up by credible analysis and experience ("heritage" in
space speak).   In general, the perception is that "more parts = more
potential failure points = higher risk" so it's gotta be a "this is the ONLY
way to make the measurement" or it's not going to fly.

You're going to spend years and years getting ready to go, and you can't go
fix it if it breaks.  Spaceflight is a very, very, very different conceptual
and planning model. (we won't even get into what you have to do if it's
connected to human space flight in any way...).  The time from "great idea"
to "mission launch" is probably in the area of 5-7 years.  The CPU flying on
the Mars Rovers is a Rad6000, which is based on an old MIPS processor.
Current missions in planning and development use things like PowerPC750's
(derated) and Sparc7s and 8's (aka ERC32 and/or LEON) and ADSP21020 clones.
Nobody is thinking about flying ARMs or Transmetas or even Pentiums.  The
popular scheme these days is various and sundry microcores (6502, 8051,
PPC604s) in Xilinx megagate FPGAs.

Actually, though, the fact that only these relatively low powered
(computationally) processors are what are flying is what makes clusters
attractive.  If you need hundreds of megaflops to do your measurement,
you're only going to get it with multiple processors.

Jim Lux

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