[Mpi3-rma] [EXTERNAL] Re: Disp_unit in allocate_shared should be returned by win_shared_query?

[Rajeev Thakur]

If there is no objection from Forum members to the addition of the parameter at a late stage (July mtg), we can leave it in there. If there is objection, we can revert back to the original version since the information is available via MPI_Win_get_attr.

Rajeev


On Jul 25, 2012, at 1:45 PM, Jim Dinan wrote:

> Hi All,
> 
> We should try to reach a decision on this issue before the end of the week.  I think it would be helpful to hear some other opinions.  So far, we have three options to choose from:
> 
> 1) Require that the displacement unit be the same at all processes for MPI_Win_allocate_shared().
> 
> 2) Allow different displacement units at each process in shared memory windows and allow processes to determine the displacement unit at remote processes via MPI_Win_shared_query().  This is in addition to the MPI-2 self-query already possible with MPI_Win_get_attr(MPI_WIN_DISP_UNIT).
> 
> 3) Allow different displacement units at each process in shared memory windows and provide only the MPI-2 self-query already possible with MPI_Win_get_attr(MPI_WIN_DISP_UNIT).  Manual communication would be needed to exchange disp_unit information.
> 
> 
> A (very) rough summary of the discussion on this issue:
> 
> * Given that non-uniform disp_unit values are currently allowed, processes may need to use disp_unit in address calculations.
> 
> * Requiring programmers to use the disp_unit at each process in address calculations diminishes the usefulness of the shared memory programming model.  It's also not clear if there is a use case to support the non-uniform disp_unit model.
> 
> Thanks,
> ~Jim.
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