[mpi3-coll] New nonblocking collective intro text

[Torsten Hoefler]

Jesper,
> > As described in Section ?? (Section 3.7), performance on many systems 
> > can be improved by overlapping communication and computation. 
> > Nonblocking collectives combine the potential benefits of nonblocking 
> > point-to-point operations to exploit overlap and to avoid 
> > synchronization with the optimized implementation and message scheduling 
> I'm not sure "optimized implementation" here really conveyes to the
> user the advantage of NBCs
hmm, this seems fine to me - you can propose a better wording, but I
think it's of marginal importance. 

> > provided by collective operations [1,4]. One way of doing this would be 
> > to perform a blocking collective operation in a separate thread. An 
> > alternative mechanism that often leads to better performance (e.g., 
> > avoids context switching, scheduler overheads, and thread management) is 
> > to use nonblocking collective communication [2].
> "the use of"
I'd prefer to stay consistent to p47:46

Best,
  Torsten

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Torsten Hoefler       | Postdoctoral Researcher
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