[Beowulf] Strange Opteron 2350 performance: Gaussian-03

[Mikhail Kuzminsky]

I'm runnung a set of quad-core Opteron 2350 benchmarks, in particular 
using Gaussian-03 (binary version from Gaussian, Inc, i.e. translated 
by more old - than current - pgf77 version, for Opteron target).

I compare in particular *one core* of Opteron 2350 w/Opteron 246 
having the same 2 Ghz frequency and the same amount of cache per core 
(512K L2 + 0.25*2 MB L3 for Opteron 2350 is just 1 MB L2 for Opteron 
246). Opteron 246 has even more fast DDR2-667 RAM.

The Gaussian-03 performance in some cases is close for both Opteron's 
(I remember that compilation didn't know about Barcelona !), but for 
very popular DFT method Opteron 2350 cores looks as slow: one job 
gives 33% more bad (than Opteron 246) performance. 

But on standard Gaussian-03 test397.com DFT/B3LYP test: *one* (1) 
Opteron 2350 core run 15667 sec. (both startstop and cpu) vs 8709 sec. 
on (one) Opteron 246 !! 

There is no powersaved daemon, so the frequnecy of Opteron 2350 is 
fixed to 2 Ghz. I reproduced this result twice on Opteron 2350, in 
particular one time using forced good numactl behaviour. I'm 
reproducing it on Opteron 246 again :-) but I have indirect 
confirmation of this timings (based on 2-cpus Opteron 246 parallel 
test).

Yes, AFAIK DFT method is cache-friendly, and more slow L3 cache in 
Opteron 2350 may give more bad performance. But in 1.8 times ??

Any your comments are welcome.

Mikhail Kuzminsky
Computer Assistance to Chemical Research Center
Zelinsky Institute of Organic Chemistry
Moscow