[Mpi3-rma] MPI-3.1 consideration slides

[Pavan Balaji]

On 12/02/2012 05:27 AM US Central Time, Torsten Hoefler wrote:
> The only thing I disagree to is slide 6. Win_sync really does nothing
> in the separate case. Your example would work on shared memory if
> flush issues a memory barrier *and* MPI_Barrier() is an optimization
> barrier (which is is in C and needs to be ensured in Fortran anyway).
> But we can discuss next week.

The problem here is that MPI_BARRIER is a process barrier, not a memory
barrier.  FWIW, with current compilers, which do not reorder
instructions across functions, this should work correctly.  But this is
a correctness concern when compilers do more than that, e.g., IPC
optimizations.

An alternative would be to leave it as-is, and add a note that we assume
the compiler will not reorder instructions here because it's a function
call, though I don't prefer this alternative.

 -- Pavan

-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji