(j3.2006) (SC22WG5.3658) N1755: Request for new features from MPI Forum
Tue Nov 11 13:14:11 EST 2008
N.M. Maclaren wrote:
>> We should explicitly allow a variable with the ASYNCHRONOUS attribute to
>> be modified or examined by means external to the processor, similarly to
>> VOLATILE variables. If such a variable is modified or examined externally
>> during a segment, that variable must not be referenced or define during
>> that segment.
> That will introduce performance implications, though perhaps less
Can you be more specific please?
> But I really don't like the idea of having to teach kiddies about
> coarrays when they want to learn MPI.
You don't have to. Segments make sense even without co-arrays, as a way
to control optimizations (code motion) in order to facilitate
interaction with "things" not visible to the compiler.
> What is actually needed is a way of allowing user code to set and clear
> a variable's pending state, in the sense used in 9.6.4. While it would
> be a bit tricky to add to Fortran, it would be semantically clean, and
> be as efficient as possible.
Sure. But, I can bet that others will have a different feeling about
what is "clean" and "efficient". This seems to be the problem here---we
are not likely to make any progress...and the issue will remain.
Imperfect is better than non-existent, IMO.
Aleksandar Donev, Ph.D.
Lawrence Postdoctoral Fellow @ LLNL
High Performance Computational Materials Science and Chemistry
E-mail: donev1 at llnl.gov
Phone: (925) 424-6816 Fax: (925) 423-0785
Address: P.O.Box 808, L-367, Livermore, CA 94551-9900
More information about the J3