CPUs for a Beowulf

Robert G. Brown rgb at phy.duke.edu
Mon Sep 8 13:00:59 EDT 2003


On Mon, 8 Sep 2003, Jim Lux wrote:

> RGB's book at the Duke Brahma site (I'm sure he'll post the URL) covers 
> some of these tradeoffs..

http://www.phy.duke.edu/brahma

But I think that Jim is optimistic that it does any better than his own
stuff below.  It hasn't been updated to take new architectural
improvments into account, and I REALLY need to add more infrastructure
stuff there as well.

However, other links on the brahma site and my personal home page do
address infrastructure at least some, as does an article I wrote for
Linux Magazine back in June.  Not so much single vs dual per se, but in
general.

Jim's refocussing your energy on overall infrastructure rather than CPU
architecture per se is dead on the money, though.

   rgb

> 
> You've posed an interesting question, because it's in the generic "what's 
> the best way to get lowest dollars per instruction executed" way, but 
> trickier..
> 
> It's that sticky word "performance"  which is the problem. Wwe can all 
> agree on what dollars mean and how much they are worth now, and in the 
> future. However, performance is different things to different people.
> 
> Is time worth money?  (that is, is there a "wall clock time" as well as a 
> CPU cycles aspect... Older computers are cheaper in terms of executing a 
> particular number of instructions, but consume more support infrastructure 
> (cooling, staff time, etc.) because, if nothing else, they have to run 
> longer...)
> 
> Is capital cost important, and, are intermediate results of interest.. 
> There's a well known example where you have a "really big problem" that you 
> could either spend some money now, and compute for the next two years, or 
> save your money, wait a year, buy the (twice as fast) computers for the 
> same price and do the computation then, finishing at the same time.  Of 
> course, you don't get any results during the first year, and for many 
> applications, the partial results early are used to guide the later work.
> 
> What's your particular labor/hardware maintenance/capital investment 
> tradeoff.. If you have copious FREE and SKILLED labor, the trade is 
> different...  Likewise, if you have a "hard" reliability requirement and 
> can't tolerate partial (or complete) downtime, the trade is different.
> 
> 
> Cluster computing, in some forms, also lends itself to "stealth, 
> below-the-funding-watchdog-radar" work.  You can buy, borrow, collect, 
> etc., CPUs and gradually add them to an ever growing configuration. I 
> notice though, that the whole cluster computing thing is a validated way to 
> work, these days, and anyone with real work to do, and the budget to pay 
> for it, just goes out and builds a real Beowulf.
> 
> 
> At 09:58 AM 9/8/2003 -0400, Robert Kane wrote:
> >Good morning,
> >
> >   If anyone doesn't mind, may I ask a few questions. When given a
> >specific application for which a cluster is being built it should be
> >relatively simple to look are the requirements of the problem and the
> >available hardware, and then determine which hardware solution is best
> >for the problem. However, if the cluster is being built as a general
> >purpose cluster for research, things become a bit more difficult, as (as
> >I far as I can tell) there is no one answer. But, if anyone has any
> >insight into the following problems it would be greatly appreciated.
> >
> >1. Single versus Dual CPUs?
> >
> >   Both of these choices have their pros and cons and are each best
> >suited for different types of problems. Given that the cluster will be
> >used for a variety of problems, is there one which would be a better
> >choice? Is there a particular configuration for which the majority of
> >problems will run better? Is there a solution that on average provides
> >more performance per dollar?
> >
> >2. CPU Type
> >
> >   Intel and AMD's new 64-bit processors are finally beginning to become
> >more common it appears. And from what I've seen the benchmarks are
> >rather impressive. However, there seems to be a significant price
> >increase going from previous generation chips (ie Xeon) to the new
> >64-bit chips. In general is the increased performance worth the money
> >invested, or would a larger number of slower chips be effective
> >cost/performance wise? Apart from the increased electricial, A/C costs
> >of course.
> >
> >
> >Thank you for any information concerning these issues, whether
> >information be answers or links to good resources,
> >
> >Robert Kane
> >_______________________________________________
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> 
> 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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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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