[Beowulf] Simple Cluster

Robert G. Brown rgb at phy.duke.edu
Mon Dec 15 13:56:04 EST 2003


On Mon, 15 Dec 2003, Andrew Latham wrote:

> I have a small 9 node p133 cluster. It works.
> 
> What does the list think about the idea of developing software on the
> smaller(mem) and older systems. I have one so I am bias but I do see that
> developing software that can handle 64meg of ram on a P586 system would lend to
> tighter and more efficant code. I am not trying to sell the P133 systems, only
> thinking about good code for them would be really nice(fast) on a Xeon or
> better. I already know this could spark a discussion on busses and chipsets and
> processors. Just thinking

More likely a discussion on balance.  I actually think that developing
on small clusters is good, but I'm not so sure about small REALLY old
systems.  The problem is that things like memory access speed and
pipelining change so much across processor generations that not only are
the bottlenecks different, the bottlenecking processes have different
thresholds and are in different ratios to the other system performance
determiners.  Just as performance on such a cluster would not be
terribly good as a predictor of performance on modern cluster from a
hardware point of view, it isn't certain that it would be all that great
from a software point of view.

My favorite case study to illustrate the point is what I continue to
think of as a brilliant piece of code -- ATLAS.  Would an ATLAS-tuned
BLAS built on and for a 586 still perform optimally on a P4 or Opteron?
I think not.  Not even close.  Even if ATLAS-level tuning may be beyond
most programmers, there are issues with stride, cache size and type, and
for parallel programmers the relative speeds of CPU, memory, and network
that can strongly affect program design and performance and scaling.

So I too have a small cluster at home and develop there, and for a lot
of code it doesn't matter as long as one doesn't test SCALING there.
But I'm not sure the code itself is any better "because" it was
developed there.

Although given that my beer-filled refrigerator is just downstairs, it
may be...;-)

   rgb

> 
> 
> --- Jim Lux <James.P.Lux at jpl.nasa.gov> wrote:
> > Outstanding, Ranjit...
> > Great that you wrote up a page describing how you did it, too!! Especially, 
> > describing the problems you encountered (i.e. slot dependence for network 
> > cards..)
> > 
> > So now you can say you built your own supercomputer.  How cool is that.
> > 
> > Jim
> > 
> > 
> > At 01:54 PM 12/15/2003 +0000, Ranjit Chagar wrote:
> > >Hi robert/jim,
> > >
> > >Well I built a cluster just for the hell of it. And as you said, before the
> > >flames start, it was built just to see what I could do, built from cheap
> > >PCs, just for the fun of it. They are 133Mhz PII and I built mine following
> > >the instructions from pondermatic. Okay, so in this day and age that is old
> > >hat, and so is my system but I enjoyed building it and enjoy playing around
> > >with it. And then, being stupid myself, I wrote out instructions so that I
> > >could did it again cause I will be the first to admit my memory isn't that
> > >good.
> > >
> > >Full details at http://homepage.ntlworld.com/ranjit.chagar/
> > >
> > >Robert - if you have any questions let me know.
> > >
> > >Jim - I dont mean for this email to sound bad but my english sometimes is
> > >taken wrong. I mean to say that you can do it if you want.
> > >
> > >Best Regards, Ranjit
> > 
> > James Lux, P.E.
> > Spacecraft Telecommunications Section
> > Jet Propulsion Laboratory, Mail Stop 161-213
> > 4800 Oak Grove Drive
> > Pasadena CA 91109
> > tel: (818)354-2075
> > fax: (818)393-6875
> > 
> > _______________________________________________
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> =====
> /---------------------------------------------------------------------------------------------------\
> Andrew Latham -LathamA - Penguin Loving, Moralist Agnostic.
> 
> What Is an agnostic? -  An agnostic thinks it impossible to know the truth
> in matters such as, a god or the future with which religions are concerned 
> with. Or, if not impossible, at least impossible at the present time.
>  
> LathamA.com - (lay-th-ham-eh) - lathama at lathama.com - lathama at yahoo.com
> \---------------------------------------------------------------------------------------------------/
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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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