Added comment: Two cpu intensive Windows threads run parallel in the two cores...100%
Paul M. Grant, PhD Principal, W2AGZ Technologies Visiting Scholar, Applied Physics, Stanford University EPRI Science Fellow (Retired) IBM Research Staff Member Emeritus w2agz at pacbell.net http://www.w2agz.com ? ? -----Original Message----- From: pw_forum-bounces at pwscf.org [mailto:[email protected]] On Behalf Of Paul M. Grant Sent: Saturday, February 09, 2008 12:23 PM To: 'PWSCF Forum' Subject: Re: [Pw_forum] multi core Vs Single core For what it's worth, here're some anecdotal experiences I've had over the last several days on an AMD64x2 HP Pavilion box I got real cheap. I've haven't installed Kubuntu yet, but running some of my benchmarks under Cygwin/X (Win OS is Vista 32 bit), it seems "cpu intensive" tasks, like gfortran compile and pwscf nscf run only in one core...(~50% cpu as shown by Task Manager) with certain Vista "services" occasionally launching, presumably in the other core, ramping the total to 100%. BTW, the max commitment of RAM is only 50% of the that available, and there is very little disk activity. It will be interesting to see how Kubuntu handles this. Paul M. Grant, PhD Principal, W2AGZ Technologies Visiting Scholar, Applied Physics, Stanford University EPRI Science Fellow (Retired) IBM Research Staff Member Emeritus w2agz at pacbell.net http://www.w2agz.com ? ? -----Original Message----- From: pw_forum-bounces at pwscf.org [mailto:[email protected]] On Behalf Of Axel Kohlmeyer Sent: Friday, February 08, 2008 9:34 AM To: PWSCF Forum Subject: Re: [Pw_forum] multi core Vs Single core 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. _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list Pw_forum at pwscf.org http://www.democritos.it/mailman/listinfo/pw_forum
