[Beowulf] Max flops to watts hardware for a cluster

Jim Lux james.p.lux at jpl.nasa.gov
Mon Feb 16 16:00:34 EST 2004


This is an exceedingly sophisticated question..

Do you count:
Wall plug watts to flops? or CPU watts to flops?
does the interconnect count?  (just the power in the line drivers and
terminations is a big power consumer for spaceflight hardware... why LVDS is
overtaking RS-422 ... 300mV into 100 ohms is a lot better than 12-15V into
100 ohms. Too bad LVDS parts don't have the common mode voltage tolerance.

I'll bet that gigabit backplane in the switch burns a fair amount of
power...

does the memory count?  This would drive more vs less cache decisions, which
affect algorithm partitioning and data locality of reference.

Is there a constraint on a "total minimum speed" or "maximum number of
nodes"?  The interesting tradeoff in speed of nodes vs number of nodes
manifests itself in many ways: more interconnects, bigger switches, etc.

More nodes means Larger physical size means longer cables means more cable
capacitance to charge and discharge on each bit means more power in the line
drivers.

What's your message latency requirement?  Can you do store and forward
through the nodes (a'la iPSC/1 hypercubes) (saving you the switch, but
adding some power in the CPU to shuffle messages around)

Can free space optical interconnects be used?  (power hungry Tx and Rx, but
no cable length issues)


Anyway.. this is an issue that is very near and dear to my heart (since I'm
designing power constrained systems).  One problem you'll find is that
reliable and comparable (across processors/architectures) numbers are very
hard to come by.  I've spent a fair amount of time explaining why 40 MFLOPs
in a 20 MHz DSP can actually be a lot more "crunch" at a lot less power than
a 200 MIPS PowerPC 750 running at 133 MHz.


Jim Lux
Spacecraft Telecommunications Section
Jet Propulsion Lab


----- Original Message -----
From: "Camm Maguire" <camm at enhanced.com>
To: <beowulf at scyld.com>
Sent: Monday, February 16, 2004 7:47 AM
Subject: [Beowulf] Max flops to watts hardware for a cluster


> Greetings!  The subject line says it all -- where can one get the most
> bang per watt among systems currently available?
>
> Take care,
> --
> Camm Maguire      camm at enhanced.com
> ==========================================================================
> "The earth is but one country, and mankind its citizens."  --  Baha'u'llah
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