Re: [mpi-21] Proposal: Non-blocking collective operations for MPI-3

[Gil Bloch <gil@xxxxxxxxxxxxxxxxxx>]

Torsten Hoefler wrote:
> Dear Jesper, all,
>   
> > it is in my opinion a very severe (and limiting) constraint that
> > you require that non-blocking and blocking collectives must match (p. 5) -
> > as we have discussed many times.
> >     
> Yes, thanks for mentioning this. I (kind of) agree on this - this
> proposal is very preliminary to get the discussion started. We
> established a working group on "extended collectives" at the forum. We
> will decide on things liks this in the group and everybody is free to
> join (just let me know if you're interested).
>   
I would like to join the "extended collectives" working group. I had to 
skip January meeting but I do plan to attend the later meetings.
>   
> > As argued in my comments on topological collectives, I think non-blocking
> > collectives belong in a seperate library on top of MPI, and the task of
> > the MPI standard is "just" to make sure that this can be implemented 
> > efficiently (they could somehow be associated with MPI as an "auxiliary 
> > library" - there might be benefits to that?)
> >     
> I do also agree on this and am in favor of the "MPI 0.5" or "Mini-MPI" or
> however you will call it. But we have to consider that this could be
> very confusing. We have the blocking collectives *in* the standard and
> the non-blocking variants, that are semantically very close, as a
> separate library. And things like MPI/IO that could perfectly be done as
> a separate library (cf. ROMIO) are also *in* the standard. That could be
> very confusing to users and would seem inconsistent to me. 
>   
I agree, and I think we should have non-blocking collectives *in* the 
standard and not as an extension to prevent the confusion and to have 
all the collective semantics in one place.

- Gil