On Tue, Apr 24, 2012 at 4:24 PM, William Gropp <[email protected]> wrote:

Yes, an MPI process need not be an OS process, and there is in fact a long history of such implementations, starting (as far as I know) with TMPI. �An easy out is to make this optional and only apply when there is such a one-to-one mapping of MPI and OS processes.

I believe in those "threaded MPI task" environments, internally inside the MPI library there is still a way to tell a process (and the thread group inside that process) on particular host where to start from. I think it is more straightforward than communicating the RANK during MPI_Init() from an MPI implementer point of view. So whoever starts the MPI tasks on a node should be able to set something unique in the environment... And BTW, thanks William & Rob Ross for sending me the MPITypes library 2 years ago. I played with it for a while and I will eventually go back to it! Rayson ================================= Open Grid Scheduler / Grid Engine http://gridscheduler.sourceforge.net/ Scalable Grid Engine Support Program http://www.scalablelogic.com/

Bill

William�Gropp Director, Parallel Computing Institute Deputy Director for Research Institute for Advanced Computing Applications and Technologies Paul and Cynthia Saylor Professor of Computer Science University of Illinois Urbana-Champaign

On Apr 24, 2012, at 12:46 PM, John DelSignore wrote:

I'm not familiar with any implementations where there are multiple MPI processes per OS process. I did read Snir's proposal, but I can't say that I'm less confused about what it implies relative to an MPI process's rank in MPI_COMM_WORLD. Are you saying that a single OS process may have contain multiple MPI processes where each MPI process has a unique rank in MPI_COMM_WORLD? And therefore, if we try to use the environment to identify an OS process's rank in MPI_COMM_WORLD, it would have to be more like a list of ranks rather than a single value?

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