Problems with parallel scaling

Clicked A Few Times	6:25:08 AM PDT - Tue, Jun 10th 2014 Hello, we are having problems with parallel scaling of NWChem on our supercomputer. We measured little or no parallel speedup with small test cases running on 1-128 CPUs. For example, times for examples/qmd/3carbo.nw : NCPU time[s] 1 401,509 2 276,147 4 193,832 8 119,013 16 118,552 32 228,424 64 331,187 128 1362,602 Other tests show worse results, for example calculating energy of (H2O)2 H: aug-cc-pVDZ, O: aug-cc-pVTZ, CCSD, the time of parallel calculation is always worse than when using only 1 CPU. The computer is a Linux x86_64 cluster with Infiniband (Anselm). NWChem version 6.3-rev2, compiled with Intel. We tested both Intel MPI and Open MPI. Is there some problem with our configuration or the input systems are just too small for NWChem parallelization? Any help would be appreciated, Martin Stachon VSB-TU Ostrava & IT4Innovations

Forum Vet	9:21:51 AM PDT - Tue, Jun 10th 2014 Martin the input you are using is very small, therefore it will never scale. Please have a look at the benchmark section on the NWChem web page for beefier input files http://nwchemgit.github.io/index.php/Benchmarks

Gets Around	11:08:55 PM PDT - Thu, Jun 12th 2014 Dear Stachon, can you test parallel scaling with input from http://nwchemgit.github.io/Special_AWCforum/st/id1298/armci_malloc%3Amalloc_1_fail... I think it sufficiently big to be scalable. You need to set the size of "memory global" to >=12Gb/n, where n is NCPU. For 1 CPU, you must increase DEFAULT_MAX_NALLOC http://nwchemgit.github.io/Special_AWCforum/sp/id4625, but for 2 or more CPU's it is not needed. P.S. Please apply the patch http://nwchemgit.github.io/Special_AWCforum/sp/id4530 for all tasks. Thanks, Vladimir

Gets Around	11:10:23 PM PDT - Thu, Jun 12th 2014 del

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