[Beowulf] recommendations for cluster upgrades

Rahul Nabar rpnabar at gmail.com
Sat May 16 18:56:15 EDT 2009

On Sat, May 16, 2009 at 2:34 PM, Tiago Marques <a28427 at ua.pt> wrote:
> One of the codes, VASP, is very bandwidth limited and loves to run in a
> number of cores multiple of 3. The 5400s are also very bandwith - memory and
> FSB - limited which causes that they sometimes don't scale well above 6
> cores. They are very fast per core, as someone mentioned, when compared to
> AMD cores.

Thanks Tiago. This is super useful info. VASP is one of our major
"users" too. Possibly 40% of the cpu-time. Rest is a similar
computational chemistry code, DACAPO.

It would be interesting to compare my test-run times on our
AMD-Opterons (Barcelona). Is is possible to share what your benchmark
job was?

Since you mention VASP is bandwidth limited do you mean memory
bandwidth or the interconnect? Maybe this question itself is naiive.
Not sure. What interconnect do you use? We have gigabit ethernet dual

A side note: I wasn't aware of VASP preferring multiples of 3 cpus.
I'm not a big VASP user myself but I see my users often submit jobs on
multiples of 8 since we have 8 cpus / box.  Is that a big drag on
performance? Why? I thought VASP parallelized over bands so could
scale well to any cpu-multiple?

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