Pardon my naivete, but why is bind-to-none not the default, and if the user wants to specify something, they can then get into trouble knowingly? We have had all manner of problems with binding when using cpusets/cgroups.
-- bennet On Thu, Sep 29, 2016 at 9:52 PM, Gilles Gouaillardet <gil...@rist.or.jp> wrote: > David, > > > i guess you would have expected the default mapping/binding scheme is core > instead of sockets > > iirc, we decided *not* to bind to cores by default because it is "safer" > > > if you simply > OMP_NUM_THREADS=8 mpirun -np 2 a.out > > then, a default mapping/binding scheme by core means the OpenMP threads end > up doing time sharing. > > this is an honest mistake (8 cores per task were not requested), so having a > default mapping/binding scheme by socket means > > OpenMP threads are spread on the socket and will likely not do time sharing. > > /* if you run on a single socket, or if you run 4 tasks on a dual socket > nodes, then (some) tasks do share the socket, > > and depending on how the OpenMP runtime is implemented, two threads of two > distinct tasks could end up bound/running on the same core */ > > > Cheers, > > > Gilles > > > On 9/30/2016 3:04 AM, David Shrader wrote: >> >> Hello All, >> >> Would anyone know why the default mapping scheme is socket for jobs with >> more than 2 ranks? Would they be able to please take some time and explain >> the reasoning? Please note I am not railing against the decision, but rather >> trying to gather as much information about it as I can so as to be able to >> better work with my users who are just now starting to ask questions about >> it. The FAQ pretty much pushes folks to the man pages, and the mpirun man >> page doesn't go in to the reasoning. >> >> Thank you for your time, >> David >> > > _______________________________________________ > users mailing list > users@lists.open-mpi.org > https://rfd.newmexicoconsortium.org/mailman/listinfo/users _______________________________________________ users mailing list users@lists.open-mpi.org https://rfd.newmexicoconsortium.org/mailman/listinfo/users
