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.
