[gmx-users] Scaling on IBM/SP2 vs. Linux/AMD

[Anton Feenstra]

Hi All,


Early this week I reported on bad scaling on an IBM/SP2 Power3 & Power4 
machine. I've continued these benchmarks, and additionally ran some on our
Linux AMD 1G-single & 1.3G-dual cluster. The system is the 120000 atom
DSSP bilayer/water system from the Gromacs benchmark suite. This makes
for a nice comparison in networking performance, since the CPU performances 
for the IBM and AMD are comparable. The IBM/SP2 should be quite well
optimized. The MPI-CH on the Linux cluster can probably be improved
(mainly the short message length setting...).

	SP2/Power3	SP2/Power4	Linux/AMD 1G	Linux/2 AMD 1.3G
#CPU	ps/hour	scale	ps/hour	scale	ps/hour	scale	ps/hour	scale
 1	 2.0	1.00	 3.9	1.00	 2.0	1.00	 3.1	1.00
 2	 4.2	1.03	 8.5	1.08	 3.9	0.98	 8.5	1.37
 3	 6.4	1.04	11.9	1.01	 4.8	0.80	 5.8	0.62
 4	 8.5	1.04	18.3	1.16	 6.5	0.82	12.1	0.97
 6	12.6	1.03	22.8	0.97	 6.0	0.51	12.6	0.67
 8	16.3	1.00	30.5	0.97	 7.3	0.46	12.4	0.50
10	20.3	1.00	37.9	0.97			11.8	0.38
16	31.3	0.96	55.0	0.88
18	34.2	0.93
20	37.0	0.91
24	42.2	0.86
28	46.8	0.82
32	50.7	0.78

No differences at 1 or 2 CPU's. Still comparable at 4 (and you can see
you shouldn't use 3 CPU's on a dual-CPU cluster; it's slower than 2!). 
But after that (at >=6 CPU's) the IBM really rules with scalings around
90% or better up to 16 (power4) or 20 (power3) CPU's! The dual AMD
nodes peak out at 6 CPU's with 12.6 ps/h. Scaling for the single AMD's
is slightly better, which should be expected since the nodes are slower.


-- 
Groetjes,

Anton
 ________ ___________________________________________________________
|        | Anton Feenstra                                            |
| .      | Dept. of Pharmacochemistry - Vrije Universiteit Amsterdam |
| |----  | De Boelelaan 1083 - 1081 HV Amsterdam - The Netherlands   |
| |----  | Tel: +31 20 44 47608 - Fax: +31 20 44 47610               |
| ' __   | Feenstra at chem.vu.nl - http://www.chem.vu.nl/afdelingen/FAR|
|  /  \  |-----------------------------------------------------------|
| (    ) | Dept. of Biophysical Chemistry - University of Groningen  |
|  \__/  | Nijenborgh 4 - 9747 AG Groningen - The Netherlands        |
|   __   | Tel +31 50 363 4327 - Fax +31 50 363 4800                 |
|  /  \  | K.A.Feenstra at chem.rug.nl - http://md.chem.rug.nl/~anton   |
| (    ) |-----------------------------------------------------------|
|  \__/  | "I'm Only Faking When I Get It Right" (Soundgarden)       |
|________|___________________________________________________________|
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