[Mpi3-rma] MPI3 RMA proposals in general

[Torsten Hoefler]

On Wed, May 26, 2010 at 12:45:45PM -0500, Douglas Miller wrote:
> 
> I must admit I have not been able to properly follow all the discussions
> going on, but as a casual observer and one-time implementer I have
> concerns.
> 
> I don't see the problems that I had trying to optimize MPI RMA
> implementations being addressed. It seems to me that having a robust API
> that can't be implemented efficiently is as bad as having an insufficient
> API.
> 
> The problems I had with MPI2 RMA seem to be centered on the fact that all
> synchronization methods could be used on the same window indiscriminately
> throughout the program. This makes it very difficult to optimize an
> implementation because of all the corner-cases and state information that
> must be dealt with. With new interfaces being heaped on top of old ones, I
> see the problem only getting worse. It really seems to me that the MPI2 RMA
> should be thrown out and redesigned.  I know that's not possible,
> especially at this late time, and I hope I have not insulted anyone by
> saying this. There's no need to respond to that statement (unless people
> actually think that's a reasonable track).
I obviously disagree but I'll not comment further :).

> But, what about having some restrictions on what synchronization that a
> window will use. I would envision either different window types altogether
> (e.g. MPI_Win_create_lock, MPI_Win_create_pscw, ...) or at least some sort
> of assert parameter (which must be specified) to establish at cerate time
> how a window will be synchronized. At the very least then, internally I
> could add a function table to the window object that selected optimized
> routines based on the window usage.
That's a good proposal and we could add this as an assertion (e.g.,
assert that I'm only using synch. mode xyz). You should propose that to
the group.

Torsten

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Torsten Hoefler         | Research Associate
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