Dear MPI RMA Group,
We have several partial MPI RMA proposals. To move forward, we need
to have a better understanding of the real needs by users, and we will
probably need to make some tough decisions about what we will support
and what we won't (as Marc has noted, some fairly obvious shared
memory operations are very tough in OpenMP, so its clear that being
universal isn't requred).
What we'd like by this *Friday* are some specific examples of
operations that are hard to achieve in MPI RMA *and* that have a clear
application need. What we *don't* want is simply "we should have a
better Put", "we need active messages", or "the implementations I've
used are
too slow". What we do want is something like the following:
We've implemented a halo exchange with MPI-RMA, and the construction
of the Memory windows is awkward and limiting, particularly if the
domains are created dynamically, making it hard to create the memory
windows collectively. We need either a method that lets us export a
local window or a way to allow all processes to refer to one single
window (something like the MPI_WIN_WORLD proposal). Example code can
be found at <url here> (or post on wiki).
or
We need a fetch and increment (or something similar) to implement a
remote lock that will allow us to make a complex series of remote
updates (and accesses) atomically that are needed for <specific
application description here>. As shown in Using MPI-2, while a fetch
and increment is possible in MPI-RMA, it is extremely complex and
awkward.
We'll take these examples and compare them to the current proposals
and the original MPI RMA in order to evaluate where we are.
Again, please send us your concrete requirements by Friday, Feb 5th.
Thanks!
Bill and Rajeev
William Gropp
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign
