I want to make everyone on the 2.2 list aware of this update to ticket #117: Thanks, Dave Solt -----Original Message----- From: MPI Forum [mailto:mpi-22_at_[hidden]] Sent: Monday, May 11, 2009 12:52 AM Subject: Re: [MPI Forum] #117: Define a new MPI_Count Datatype #117: Define a new MPI_Count Datatype ----------------------------+------------------------------------------- ----------------------------+---- Reporter: kannan | Owner: davesolt Type: New routine(s) | Status: new Priority: Had 1st reading | Milestone: 2009/06/08 California Version: MPI 2.2 | Resolution: Keywords: | Implementation: Waiting ----------------------------+------------------------------------------- ----------------------------+---- Changes (by davesolt): * owner: kannan => davesolt Comment: I have reassigned this to me as my colleague, Kannan, has moved on to a different role within HP. I have been working to come up to speed on this ticket and provide a reference implementation with Open MPI, which I have made available at: http://bitbucket.org/jsquyres/mpi-count/ Thanks to Jeff S. for his help on setting this up. The implementation is for C and Fortran 90. It does not include C++, although I have manually verified that C++ does work in the same way. The goal of this prototype is to demonstrate that applications can be compiled with a header file that uses the previous interface definitions and then dynamically linked against an MPI that uses the new interfaces. However, this implementation reflexively demonstrates the feasibility because only the header files where changed. Therefore, an application compiled with this implementation will be compiled against a different header file than the associated library uses for its own definitions. For example, the mpi.h header file defines MPI_Send with an MPI_Count argument. Internally, the library defines MPI_Send using an int argument. Applications compiled against this header file will run with this implementation, proving that the header file difference does not actually change the signatures in a significant way. In addition, an application compiled with the "old" header file will run against this implementation. There are example files in the 117 directory to test with. In the course of this work I did come to wrestle with some of the same issues brought up on this list: 1) MPI_Type_size, etc.

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What about MPI_Type_size now that all the datatype constructors take MPI_Count?

My rationale -- I'd left out converting size arguments/return values on other APIs >since I targetted MPI_Count to represent only the count type, and not get into the >promotion of sizes. I agree that logically MPI_Type_size has to be promoted, but >that would mean that we would now have to go thru every API that takes in/ returns >sizes and look for candidates.

I also found it difficult to draw a line at what other arguments need to be converted to account for the fact that the proposal allows for large datatypes. In retrospect, I wish that the proposal had not attempted to allow for large datatypes and had limited itself to communicating calls. Some other calls such as MPI_Unpack and MPI_Type_size are clearly incompatible with the proposed changes. 2) MPI_Type_get_envelope, MPI_Type_get_contents I believe that since these return values that were set by creation routines, some of these arguments need to be MPI_Count sized as well. In the prototype implemenation, I did change these arguments, but have not yet made any changes to this proposal 3) MPI_Type_create_struct The proposal is to change argument #1, but I believe this is incorrect. Argument #1 is the number of items in the struct, which is likely to not be > 2GB. However, the 2nd argument is the size of individual elements, which I believe is the argument we intend to change. 4) MPI_Status_set_elements This is not included in the proposal, but I believe that argument #3 should clearly be MPI_Count sized since the proposal is that the count field of status can be > 2GB. 5) MPI_Type_create_darray I believe this was an oversight and this datatype creation routine should have argument #3 changed to MPI_Count. I would appreciate some other input on this one as I do not have a lot of experience with this particular function. -- Ticket URL: <https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/117#comment:38> MPI Forum <https://svn.mpi-forum.org/> MPI Forum