On Fri, Dec 01, 2006 at 09:35:09AM -0500, Brock Palen wrote: > On Dec 1, 2006, at 9:23 AM, Gleb Natapov wrote: > > > On Fri, Dec 01, 2006 at 04:14:31PM +0200, Gleb Natapov wrote: > >> On Fri, Dec 01, 2006 at 11:51:24AM +0100, Peter Kjellstrom wrote: > >>> On Saturday 25 November 2006 15:31, shap...@isp.nsc.ru wrote: > >>>> Hello, > >>>> i cant figure out, is there a way with open-mpi to bind all > >>>> threads on a given node to a specified subset of CPUs. > >>>> For example, on a multi-socket multi-core machine, i want to use > >>>> only a single core on each CPU. > >>>> Thank You. > >>> > >>> This might be a bit naive but, if you spawn two procs on a dual > >>> core dual > >>> socket system then the linux kernel should automagically schedule > >>> them this > >>> way. > >>> > >>> I actually think this applies to most of the situations discussed > >>> in this > >>> thread. Explicitly assigning processes to cores may actually get > >>> it wrong > >>> more often than the normal linux scheduler. > >>> > >> If you run two single threaded ranks on the dual core dual socket > >> node > >> you better be placing them on the same core. Shared memory > >> communication > Isn't this only valid with NUMA systems? (large systems or AMD > Opteron) The intel multicores each must communicate along the bus to > the north-bridge and back again. So all cores have the same path to > memory. Correct me if im wrong. Though working on this would be > good, i dont expect all systems to stick with bus, and more and more > will be NUMA in the future. AFAIK Core 2 Duo has shared L2 cache so shared memory communication should be much faster if two ranks are on the same socket. But I don't have such a setup to test the theory.
> > On another note for systems that use pbs (and maybe other resource > managers) It gives out the cpus in the hostlist (hostname/0 > hostname/1 etc) Why cant OMPI read that info if its available? > > Im prob totally off on these comments. > > Brock > > > I mean "same socket" here and not "same core" of cause. > > > >> will be much faster (especially if two cores shares cache). > >> > >>> /Peter (who may be putting a bit too much faith in the linux > >>> scheduler...) > >> Linux scheduler does its best assuming the processes are > >> unrelated. This is > >> not the case with MPI ranks. > >> > >> -- > >> Gleb. > >> _______________________________________________ > >> users mailing list > >> us...@open-mpi.org > >> http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > -- > > Gleb. > > _______________________________________________ > > users mailing list > > us...@open-mpi.org > > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Gleb.
