On 09/23/2011 12:47 PM, Barrett, Brian W wrote:

It might not be able to. If non-coherent load/store is byte access (or word access), it can provide a separate public and private window in separate and meet the semantics. If it provides cacheline access to non-coherent space, it will not be able to provide shared memory across uncached space; such is the cost of standardization.

Do we know any non-cache-coherent system that provides byte access (note that word access is not sufficient)? What I'm arguing is that we are not giving any additional flexibility for non-cache-coherent systems with this new "clarified semantics". In fact, we are making it more difficult for future MPI versions to actually define a semantics by saying that "multiple remote stores to the same window have to work" -- we'll be stuck with this if we say that in the standard now. Instead, if we leave it undefined, in MPI-3.1 (or 4.0), we might be able to separate out local load/store and remote load/store operations and say that multiple remote load/store operations is undefined (or erroneous or whatever). So the options I'm proposing are: 1. Either define remote load/stores in SEPARATE. (or) 2. Leave it as undefined. Attempting a half-definition is making it worse than leaving it undefined. -- Pavan -- Pavan Balaji http://www.mcs.anl.gov/~balaji