Yes, and it is unfortunate that there is a dearth of representative platforms. However, MPI-2 RMA worked to get this right and it's generally accepted that those semantics support non-coherent platforms, so in the absence of an argument that MPI-2 RMA semantics don't work for non-coherent platforms, I would argue that we can just use those. Jeff On Mon, Dec 3, 2012 at 7:55 AM, Jim Dinan <[email protected]> wrote:
On 12/3/12 9:44 AM, Jeff Hammond wrote:
On Mon, Dec 3, 2012 at 7:39 AM, Jim Dinan <[email protected]> wrote:
On 12/2/12 7:44 AM, Jeff Hammond wrote:
(1) Define semantics of shared memory windows in separate model.
In Section 11.2.3 it says "MPI does not define semantics for accessing shared memory windows in the separate memory model."
I would like to try to define these semantics in MPI 3.1. Shouldn't it at least be possible to use MPI_WIN_(UN)LOCK with MPI_LOCK_EXCLUSIVE here?
I believe that supporting RMA for weakly- or non- coherent memory architectures is vital for future systems.
I agree. We had this discussion and decided to postpone it because we had other more pressing issues. Now may be the time. A discussion would be good.
Yes, there was no urgency. I'm glad the standard left this issue wide open instead of defining something restrictive.
IMHO, defining shared memory windows in the separate model is not a worthy use of the Forum's time. This will be hard to get right, and AFAIK no (reasonable) system requires it. As we've currently left it, if this functionality is needed, one can define the semantics as an MPI extension. I think this is a better option that defining a new model in the absence of a platform that uses it.
Intel SCC is non-coherent but supports POSIX shared memory. It's really quite simple to use there, but one has to have synchronization primitives. I just want the Forum to define those in the same manner as for MPI-2 RMA, which supports non-coherent platforms.
What's the harm in saying that MPI_WIN_UNLOCK approach causes global visibility of the window to all processes?
I think that what you suggested would be a useful and reasonable extension to an MPI implementation. However, the SCC is still a research prototype; I don't think it has reached the level of maturity needed to define semantics in a standards document.
~Jim. _______________________________________________ mpi3-rma mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
-- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute [email protected] / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond