On Feb 8, 2008 12:10 PM, Marcel Mohr <marcel at physik.tu-berlin.de> wrote: > There are some posts about this topic some time ago. > > Planewave codes use a lot of memory bandwith, so an Intel > quadcore is not much faster than a dual core on the same mainboard, > because the memory bus becomes the bottleneck of the system, and all core > share the same bus.
for some additional numbers on multi-core. have a look at: http://groups.google.com/group/cp2k/msg/aa1ce54b56598aab?dmode=source FYI, CP2K/QuickStep is even more demanding in terms of memory bandwidth than QE. however, since some vendors are offering quad-core nodes for about the same price as dual-core nodes, it is actually a better deal to get quad-core and then use only half of the cores (and have twice the cache) if you get processor affinity set up right. a. > > Cheers > Marcel > > > On Fri, 8 Feb 2008, Axel Kohlmeyer wrote: > > > On Fri, 8 Feb 2008, ambavale sagar wrote: > > > > > > sagar, > > > > AS> Is multi (quad) core processor more efficient than single core for our > > > > please clarify what you mean by "efficient". > > more throughput for the same money, faster execution, > > better utilization of the cpu, less room needed for > > a given computational capability? > > > > AS> abinitio calculations? How efficiently multi-threading is done while > > AS> working with serial version of code on multicore machine? > > > > it is a common misconceptions that you need to use multi-threading > > to take advantage of multicore cpus. the vendors of those cpus > > are somewhat promoting it, because it is simpler to add multi-threading > > to a code than to parallelize it completely, and also because > > their new cpus don't have any advantage over the older ones without > > paralleization. fortunately, the methods used in quantum espresso > > are well parallelizable and the code offers multiple levels of MPI > > parallelism which i found to be almost always more efficient than > > using OpenMP (and thus multi-threading). even more so, QE does not > > support OpenMP (only indirectly via threaded BLAS/LAPACK libraries). > > > > depending on your hardware, problem set size and compiler/library > > combination, you can get a speedup of roughly 2.5x to 3.5x from > > a quad core cpu over a corresponding single core. when using multiple > > nodes via a network, however, the speed and the latency of the > > network (and the options of parallization, i.e. if you can parallelize > > over k-points or not) start to matter and can make it all very > > confusing. > > > > in the end, apart from a few general observations, there is no other > > way to get a definite answer than running tests with representative > > input files. > > > > cheers, > > axel. > > > > p.s.: this brings up the question again, that we should compile a > > list of such typical inputs and run them on mutually available > > machines so people can see what to expect.... > > > > AS> > > AS> Thanx. > > AS> > > AS> > > AS> > > AS> Sagar K. Ambavale > > AS> > > AS> PhD student, > > AS> > > AS> The M.S. University of Baroda, > > AS> > > AS> India > > AS> > > AS> > > AS> > > ________________________________________________________________________________ > > AS> 5, 50, 500, 5000 - Store N number of mails in your inbox. Click here. > > AS> > > > > -- > > ======================================================================= > > 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. > _______________________________________________ > 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.
