[Beowulf] CCL:Question regarding Mac G5 performance (fwd from mmccallum at pacific.edu)

[Bill Broadley]

> I had done some comparisons between price/performance, and I found dual  
> G5s to be at or near the best in price/performance, especially if  
> things are recompiled with the IBM compilers (between 8-10 % speed  
> increase over pre-compiled (with apple gcc) versions of NAMD2, and  
> using standard gcc for charmm).  I would expect that things like  
> gaussian03 run very well (I believe gaussian uses the IBM compilers for  
> macOS).  For MD, the speedup seems to be due to the on-chip square root  
> eval.

Any actual numbers would be very useful, ideally with the compilers,
compiler options, motherboard, and similar.  Did you compare 1 job per
node vs 1 job per node?  Or 2 jobs per node vs 2 jobs per node?  4 or 8
dimms?  Which kind of memory PC2700? PC3200?

> The built-in Gigabit enet is attractive, also, as charmm and NAMD scale  
> very well with gigabit, and it makes myrinet less price-effective (when  
> used on any platform, wintel included, see
> http://biobos.nih.gov/apps/charmm/charmmdoc/Bench/c30b1.html for  
> example).  I decided that dual G5 xserve cluster nodes with gigabit  

I come to a different conclusion based on those graphs.  In the first
graph myrinet improves by a factor of 2.6 (250 -> 95 seconds) from 2
processors to 8, where gige improves by only 20% (255 -> 210).  In the
second graph gigE gets SLOWER from 2 to 8 processors.  Do you think in
either case the 8 node (let alone 16) gige cluster would have better
price/performance then a myrinet cluster?

Seems like for applications like shown on that page you shouldn't
really bother with a cluster over 2 nodes with gigE, not many people
would be willing to pay a factor of 4 more for 20% or even negative
scaling.

> switches were much more cost-effective for me than any other processor,  

Cost effective = price/performance?  Can you make any numbers available?

> especially any high-bandwidth specialty comm method (apple's gigabit  
> has a pretty low latency also).

Oh?  Can you share the apple gigabit numbers?  What is "pretty low"?

> Additional considerations for us were the BSD environment which is more  
> secure than windows, and the OS is arguably more stable and supported  

I'd agree with more stable and supported for use as a desktop, I'd
disagree with stable and supported as computational node.  OSX is the
new player on the block in this space.  Do you really think you would
get a good response from calling apple's tech support line when the
scheduler or network stack isn't performing to your performance
expectations?  

Certainly a very reasonable thing.

> It is my impression that opterons, PIVs, G5s all have their advantages,  

Agreed, thus the value in sharing performance actual results for
specific codes in specific environments.

-- 
Bill Broadley
Computational Science and Engineering
UC Davis