Jeff, Thanks for your comments. A good goal for MPI-3 RMA would be to define an interface that NWCHEM would want to use directly, instead of having to rely on ARMCI. Your input in defining such an interface would be valuable. Rajeev

-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jeff Hammond Sent: Saturday, April 25, 2009 7:16 AM To: Main MPI Forum mailing list Subject: Re: [Mpi-forum] MPI One-Sided Communication

Patrick and Keith,

You both make very helpful points. Yes, I am from the Church of One-sided, but only because I've got hundreds of papers showing that one-sided implementations scale very well for my application and zero papers showing scaling for two-sided. You argue against one-sided using the prevalence of MPI-1 use, but if you look at my field, the exact same argument goes against MPI-1.

The reason I am trying to participate in the MPI-3 discussion is because whenever you all finish the standard and the various implementations, I am the one who has to develop applications with it. I don't know all the low-level issues, but what I want is something that quacks like ARMCI. If MPI-3 RMA doesn't do that, I will continue not to use MPI. The reason I wanted MPI-3 RMA to take over for ARMCI is that vendors port and tune MPI first and I don't like having to wait a year to run NWChem, etc. on the leadership-class hardware. I don't care what happens under the hood (active-messages versus RDMA, etc.) as long as I can Put, Get and Accumulate without interrupting the remote processor.

Why do almost everyone use MPI-1? Find me a syllabus for course on parallel computing which teaches one-sided anything. Find me on that doesn't teach MPI-1 exclusively. Yes, there will be a few out Berkeley for UPC, UIUC for Charm++, etc. but the overwhelming majority of parallel programming education today focuses exclusively on MPI-1. If you teach a man to fish, he will fish, not farm wheat.

I often confuse RDMA and one-sided, among other things. I am a HPC code developer not a hardware designer or NIC-protocol writer. I'd love it if someone can tell me the (accessible) book I can read to figure these things out. I'm willing to plead ignorance on some of the low-level issues here if, in return, try not to claim that everything in my field can easily be done with MPI-1, since 20 years of papers say it can't (at least easily). All I'm trying to say telling me I should be using MPI-1 instead is not an argument.

Jeff

-- Jeff Hammond The University of Chicago http://home.uchicago.edu/~jhammond/ _______________________________________________ mpi-forum mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum