[Pw_forum] newbie update

Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu
Fri Mar 6 02:12:56 CET 2009

On Thu, 5 Mar 2009, Carlo Nervi wrote:

CN> time is almost 1/3 of the wall time. I suspect that Axel
CN> is right pointing to the disk I/O. I'm afraid that to
CN> increase the performance I should set the RAID 10...

no. this cannot be I/O. this is why i suggested this example.
unlike with pw.x in some configurations, there usually is no 
significant i/o when running cp.x. 
also you have almost exactly 4x the wall time relative to 
the cpu time. are you _sure_ you are running on a machine 
with 8 cores? _and_ is that machine otherwise empty?

when running on a local 2x quad-core intel xeon E5430 2.66GHz
node, i get 42.30s CPU time,    43,87s wall time. 
with serial MKL and 8 MPI tasks.

CN> OMP=2, MPI=8
CN> v0:      CP           :  0m46.98s CPU time,     1m36.08s
CN> wall time
CN> little worse than OMP=1 and MPI=8

there is no point in oversubscribing a node. you rather
want to test, whether less than the maximum number of total
tasks per node is not giving you a better speedup.



Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
If you make something idiot-proof, the universe creates a better idiot.

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