dual Xeon issue

Santiago Muelas smuelas at mecanica.upm.es
Fri Jun 6 03:15:32 EDT 2003

I am also quite a "newby" to this beowulf-world. A couple of months ago I asked a question in this list because my program did not attained my expectations. I was convinced of an ethernet problem and asked for giga-ethernet... I receive many very nice answers, but one specially was the very right one. It came from "master" Brown. He told me to fine-tune my program before doing any other thing... and he was right.
Now, I am learning with four Ahtlon XP2200 computers and sometime I tested them against a dual 2-Xeon-2200 Dell , expensive one, plus, sometime another dual with 2 Ahtlon 1800.
So, as finally the results are --for me-- impressive and the size of my little "toy" could be similar to yours, and despite the fact that I am the perfect oppposite to an expert in clusters, here are my recomendations:
	- Do not expend money in "better" things. In this aspect, quantity is better than "theoretical-quality"
	- Normal ethernet is great and more than enough for 4,5 or 6 machines.(and an standard switch)
	- Choose the best price-quality possibility.
	- Use "xmpi" and work on your program until the "red" has almost disappeared.  

And here are my results, tested with a finite element program written by my friend Lee Margetts abd fine-tuned by him:

	- Time to run an iterative, 100.000 equations program on one Ahtlon: 58 sec. On 2 machines 37 sec.(I have limited the iterations to the minimum)
	- The same on one CPU with the Xeon: 62 sec. On 2 CPU 40 sec.

The Xeon has 1Gb. memory for each processor. The Ahtlons 512Kb each.

Now a bigger problem: 330.000 equations. In this case and due to memory requirements I was not able to run the program on just 2 Ahtlons, so I run it on the four. With the same total memory as the Dell-Xeon, I tested on this one with the two processors. Clearly, the results are not comparable but give an interesting result:

	- Time to run on the 2-Xeon: 2m56sc.
	- Time to run on the 4 Ahtlons: 1m24sc.

So less than one half.

Now, the cost: Each Athlon has 1 processor, 512Mb, one motherboard (standard with ethernet included) and one HD (chipest, but new). Total price in euros: 350-400. Cost of 4 Un. --> 1400 euros.
Dell dual-Xeon with 2Gb. total ram, scsi disk and.... 4500-5000 euros.

So the decission is simple. I will increase imediately the ram on the Ahtlons to attain 4Gb. (cost of 2 Gb= 200 euros. I use the standard cheapest OEM memory cards. Excellent, BTW)

All that means that I can have a nice beowulf with 12 computers based on Ahtlons (now Ahtlon XP 2400 has the best quality/price), for the same cost as a prestigious dual computer.

I think this is the reason of beowulf philosophy !!

Thanks to all for your patience.

On Thu, 5 Jun 2003 08:20:47 -0600 (MDT)
sfrolov at accufo.vwh.net wrote:

> Sorry for a noob-like question. We are in the process of buying a Xeon-based cluster for scientific computing (running MPI parallelized numerical models). We've benchmarked clasters offered by Microway and Aspen Systems and discovered that we are getting much better results using only one CPU per box (running the model on 6 boxes using one CPU in each box was about 50% faster than running it on 3 boxes using both CPUs). This was surprising to us since we've used to be limited by interprocessor communications, which should be a lot faster between CPUs in one box. Can anybody explain the reason for this and, more importantly, is there any way to improve this situation.
> Thanks,
> Sergei.
> P.S. Can anybody recommend the best performance/price ratio cluster?
> _______________________________________________
> Beowulf mailing list, Beowulf at beowulf.org
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Santiago Muelas
Profesor de Resistencia de Materiales y Cálculo de Estructuras
ETSI de Caminos, Canales y Puertos (U.P.M)
smuelas at mecanica.upm.es		http://w3.mecanica.upm.es/~smuelas
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