It seems to me the MPI_Get_processor_name description is too ambiguous to make this 100% portable. I assume most MPI implementations simply use the hostname so all processes on the same host will return the same string. The suggestion would work then.
However, it would also be reasonable for an MPI that did processor binding to return " hostname.socket#.core#" so every rank would have a unique processor name. The extension idea is a bit at odds with the idea that MPI is an architecture independent API. That does not rule out the option if there is a good use case but it does raise the bar just a bit. Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 From: Ralph Castain <r...@open-mpi.org> To: Open MPI Users <us...@open-mpi.org> List-Post: users@lists.open-mpi.org Date: 12/10/2010 08:00 AM Subject: Re: [OMPI users] Method for worker to determine its "rank" on a single machine? Sent by: users-boun...@open-mpi.org Ick - I agree that's portable, but truly ugly. Would it make sense to implement this as an MPI extension, and then perhaps propose something to the Forum for this purpose? Just hate to see such a complex, time-consuming method when the info is already available on every process. On Dec 10, 2010, at 3:36 AM, Terry Dontje wrote: A more portable way of doing what you want below is to gather each processes processor_name given by MPI_Get_processor_name, have the root who gets this data assign unique numbers to each name and then scatter that info to the processes and have them use that as the color to a MPI_Comm_split call. Once you've done that you can do a MPI_Comm_size to find how many are on the node and be able to send to all the other processes on that node using the new communicator. Good luck, --td On 12/09/2010 08:18 PM, Ralph Castain wrote: The answer is yes - sort of... In OpenMPI, every process has information about not only its own local rank, but the local rank of all its peers regardless of what node they are on. We use that info internally for a variety of things. Now the "sort of". That info isn't exposed via an MPI API at this time. If that doesn't matter, then I can tell you how to get it - it's pretty trivial to do. On Dec 9, 2010, at 6:14 PM, David Mathog wrote: Is it possible through MPI for a worker to determine: 1. how many MPI processes are running on the local machine 2. within that set its own "local rank" ? For instance, a quad core with 4 processes might be hosting ranks 10, 14, 15, 20, in which case the "local ranks" would be 1,2,3,4. The idea being to use this information so that a program could selectively access different local resources. Simple example: on this 4 worker machine reside telephone directories for Los Angeles, San Diego, San Jose, and Sacramento. Each worker is to open one database and search it when the master sends a request. With the "local rank" number this would be as easy as naming the databases file1, file2, file3, and file4. Without it the 4 processes would have to communicate with each other somehow to sort out which is to use which database. And that could get ugly fast, especially if they don't all start at the same time. Thanks, David Mathog mat...@caltech.edu Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ 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 -- <Mail Attachment.gif> Terry D. Dontje | Principal Software Engineer Developer Tools Engineering | +1.781.442.2631 Oracle - Performance Technologies 95 Network Drive, Burlington, MA 01803 Email terry.don...@oracle.com _______________________________________________ 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
