Hi Bill You actually can get OMPI to split a process across sockets. Let’s say there are 4 cores/socket and 2 sockets/node. You could run two procs on the same node, one split across sockets, by:
mpirun -n 1 —map-by core:pe=5 ./app : -n 1 —map-by core:pe=3 ./app The first proc will run on all cores of the 1st socket plus the 1st core of the 2nd socket. The second proc will run on the remaining 3 cores of the 2nd socket. HTH Ralph > On Jul 24, 2015, at 12:48 PM, Lane, William <william.l...@cshs.org> wrote: > > I'm just curious, if we run an OpenMPI job and it makes use of non-local > memory > (i.e. memory tied to another socket) what kind of effects are seen on > performance? > > How would you go about testing the above? I can't think of any command line > parameter that > would allow one to split an OpenMPI process across sockets. > > I'd imagine it would be pretty bad since you can't cache non-local memory > locally, > the fact both the request and data have to flow through an IOH, the local CPU > would > have to compete w/the non-local CPU for access to its own memory and that > doing this > would have to implemented w/some sort of software semaphore locks (which > would add > even more overhead). > > Bill L. > IMPORTANT WARNING: This message is intended for the use of the person or > entity to which it is addressed and may contain information that is > privileged and confidential, the disclosure of which is governed by > applicable law. If the reader of this message is not the intended recipient, > or the employee or agent responsible for delivering it to the intended > recipient, you are hereby notified that any dissemination, distribution or > copying of this information is strictly prohibited. Thank you for your > cooperation. _______________________________________________ > users mailing list > us...@open-mpi.org <mailto:us...@open-mpi.org> > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > <http://www.open-mpi.org/mailman/listinfo.cgi/users> > Link to this post: > http://www.open-mpi.org/community/lists/users/2015/07/27322.php > <http://www.open-mpi.org/community/lists/users/2015/07/27322.php>
