Setting OMP_NUM_THREAD lets you select to use multithreading or not. A slight modification of our example script on the WIEN2k faq page can even accounts for this and automatically span on eg. 8 core only 4 mpi processes (when OMP_NUM_THREAD=2).
Am 15.03.2011 15:31, schrieb Laurence Marks: > This is an informational report of an issue that can arise with Wien2k > leading to poor performance. I came across it when experimenting with > the "procs=XX" option in msub/qsub with XX=64 as an alternative to the > more standard "nodes=X:ppn=Y". > > In an scf cycle lapwdm and (with the next release) mixer always use > lapack routines (and maybe some others) which by default with mkl are > multithreaded and use multiple cores. For a mpi run with lapw0: > specified lapw0, lapw1 and lapw2 all use mpi. A issue can arise with > msub/qsub (and perhaps other) if the number of cores mkl uses is > larger than what has been allocated and there are other mpi tasks > running on the same node. Then the performance of lapwdm can be bad; > in one case rather than taking 30 seconds it took 14 minutes. > > I am not sure if this is something "fixable" in WIen2k, and there are > ways in qsub/msub to avoid it using nodes=X:ppn=Y. However, procs=XX > is "nice" as Wien2k in mpi does not really need factors of 2 > cores/node (I've tested this) and can fit in the gaps. > > N.B., running without mpi and using nodes=X:ppn=1 could also run into > the same problem. > -- P.Blaha -------------------------------------------------------------------------- Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna Phone: +43-1-58801-15671 FAX: +43-1-58801-15698 Email: blaha at theochem.tuwien.ac.at WWW: http://info.tuwien.ac.at/theochem/ --------------------------------------------------------------------------