[Mpi3-rma] Target displacement in dynamic windows
Torsten Hoefler
htor at illinois.edu
Tue Sep 18 03:02:28 CDT 2012
Hi Jim,
> In today's meeting, we arrived at the following approach to addressing
> the target displacements issue for dynamic windows:
>
> The MPI 3.0 errata should include the following two statements:
>
> 1. For dynamic windows, the target_disp argument to RMA communication
> operations is not restricted to non-negative values.
>
> 2. Users are cautioned that displacement arithmetic can overflow in
> variables with MPI_Aint type and result in unexpected values on some
> platforms. This issue will be addressed in a future version of MPI.
Sounds good!
I think we should add an additional point about
MPIX_ERR_RMA_WRONG_FLAVOR as well.
> In MPI 3.1, we will look at two possible mechanisms for providing safe
> offset arithmetic:
>
> 1. MPI_Get_pointer(MPI_Aint address, void *ptr), which will allow a user
> to convert between addresses and pointers.
>
> 2. MPI_Auint -- an address integer which can represent the full range of
> MPI_Aint as a positive integer. This could be an unsigned integer, but
> for Fortran compatibiliy, it may need to be a singed integer that's
> larger than MPI_Aint. The following conversion functions would be
> provided:
>
> MPI_Get_auint(MPI_Aint addr, MPI_Auint *uaddr)
> MPI_Get_aint(MPI_Auint uaddr, MPI_Aint *addr)
This certainly needs more discussion!
All the Best,
Torsten
--
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Torsten Hoefler | Assistant Professor
Dept. of Computer Science | ETH Zürich
Universitätsstrasse 6 | Zurich-8092, Switzerland
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