On Wed, 2009-07-15 at 13:18 +0300, Alexej Mazheika wrote: > Hi > > I apply Espresso-package under Linux with mpich2 applying it for > parallel processes calculations. The Espresso I compiled from > source-files with mpich2-compilers. I noticed a strange phenomenon. > The CPU of my PC is Intel Core Quad (64-bit). When I make my > calculations under 64-bit linux-system (openSUSE 11.0) it lasts longer > than under 32-bit one (openSUSE-11.0). For example, the average time > of SCF procedure of my task is 8 min under 64-bit OS vs 7 min under > 32-bit OS. Can this problem be binded with installation or work of > Espresso? If yes, then how to solve it? I asked the developers of > mpich2 about it, and they couldn't help me.
i don't think that this is a strange phenomenon at all. in general, a 64-bit compilation of a code should be expected to be slower than a 32-bit compilation. all memory pointers are twice the size and thus require more memory bandwidth and incur a reduced cache efficiency. only, it usually doesn't show so much on x86_64 since the 32-bit x86 cpu design is to horribly register starved and AMD doubled the number of registers to make up for it. however, if your job runs only for a few minutes then you may still see the additional overhead from the larger pointers. for a larger problem, that should be reduced. if not, there may be different compilers or compiler settings. on non-x86 CPUs a 64-bit mode compilation on codes like Q-E is typically about 10-20% slower than a 32-bit compile. cheers, axel. > > regards, > > Alex Mazheika, Research institut for Physical Chemical Problems of > BSU, Leningradskayastr. 14, 220050 Minsk, Belarus > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -- ======================================================================= 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.
