CosmoMC: how may CPUs to run is the most efficient?

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Jie Ren
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Joined: May 13 2006
Affiliation: Theoretical Physics Division, Chern Institute of Mathematics, Nankai University, Tianjin, China

CosmoMC: how may CPUs to run is the most efficient?

Post by Jie Ren » December 16 2006

Hello,
It seems not true that the more CPUs the better to run CosmoMC on a cluster. How many CPUs is the most efficient? Thank you very much for suggestions.

Antony Lewis
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Affiliation: University of Sussex
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Re: CosmoMC: how may CPUs to run is the most efficient?

Post by Antony Lewis » December 16 2006

I recommend running about 6 chains (so 6 MPI nodes), with up to 4 processors per node (openmp). I think the WMAP3 code is not really parallelized, so probably doesn't help very much having more processors per node. Personally I usually run 6x2.

Anze Slosar
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Affiliation: Brookhaven National Laboratory
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CosmoMC: how may CPUs to run is the most efficient?

Post by Anze Slosar » December 18 2006

But surely, it spends most of the time inverting matrices, so if you use MKL lapack and set OMP_NUM_THREADS to 4 it should be quite parallelised? (but in practice I've noticed suboptimal use of processors, which I couldn't explain...)

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