[mpi3-coll] Comments on nonblocking collectives section

Jesper Larsson Traeff traff at it.neclab.eu
Tue Jan 27 08:46:56 CST 2009

Dear all,

On Tue, Jan 27, 2009 at 09:28:05AM -0500, Torsten Hoefler wrote:

> Please bring it up again if you think it needs more discussion!
It doesn't, all has been said... 

> > p.50, line 20 (or elsewhere), add:
> > "Completion of a particular nonblocking collective operations does
> > \emph{not} imply completion of any other posted nonblocking collective
> > (or send-receive) operations, whether they are posted before or after
> > the operation in case."
> hmm, I think this clarification is unnecessary because similar things
> would apply to nonblocking point-to-point and are not mentioned there
> (and the semantics are clearly defined). We have Example 5.34 to make
> this clear, but I'd rather not introduce this to the introductory text.
I think it is a fairly important semantic issue, and should be said somewhere.
The (good) example comes at the end of the chapter.
> > p.50, line 24-25:
> > "cannot be defined clearly." -> "is not well-defined."
> I think that "cannot be defined" is stronger than "is not well-defined". 
yes, that's why I suggest the slightly, perhaps, weaker text

> > p.50, line 48:
> > "collective operations is required" -> "collective operation semantics
> > is required"
> I don't understand this proposal and I think the current text is
> precise.
I didn't think so, will try to come up with another wording

> > p.53, line 37:
> > "are identical as after a call" - bad Engish, should rather be:
> > "are the same as after a call".
> fixed (twice)
> > I would strongly suggest using exactly the same phrase for all of the
> > data moving collectives! This is not a document being read as a whole,
> > so we don't need to fear "repetition".
> maybe, I think the wording is clear as it is and has been reviewed
> multiple times. Thus, it should be fine. Feel free to propose a unified
> wording that does not invalidate all previous reviews ;).
I don't think it has been reviewed multiple times... ;-) it's the sort of
thing you just skip. The English (use of "identical") is in many cases
not correct...

> I'd propose to stay with the reviewed phrasing.
Maybe Bronis look it over? Again, the "identical" phrase is in my opinion
bad (but you changed that).

> > p.68, line 21: does a race condition "cause" non-determinism, or is it
> > the other way round?
> I think it's correct because it might match correctly, however, if the
> race is done in the wrong order, then it's wrong. The casual chain is
> here: programming mistake -> race condition -> nondeterminism
and that's not really what the caption says. I suggest a rewording, will
try and come up with something

> > p. 68, line 26:
> > move "outstanding" to "even if there is an outstanding nonblocking..."
> that's a matter of taste

> > p. 69, after line 34:
> > Would suggest an example 5.31 that shows that e.g. MPI_IAlltoall does
> > not match MPI_Alltoall.
> >
> > "Blocking and nonblocking collective operations do not match. The
> > following is illegal:"
> added (this should be clear after Ex 5.29, but more examples can't harm)

> I will attach it to ticket #109 after the telecon.


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