[mpi3-coll] Comments on nonblocking collectives section

Christian Siebert siebert at it.neclab.eu
Tue Jan 27 10:01:46 CST 2009

Dear all,

here are a couple of comments from my site (referring to the new version 
that Torsten sent out an hour ago):

p 4, l 26: old typo? "indentifier" -> "identifier"

p 49, l 36: question for "the communication may progress independently 
of the computations at all participating processes": What about all the 
Reduce operations which involve both communication and computation? 
Should we replace "the communication may progress" with the more general 
"the operation may progress"?

p 50, l 14: same argument as above; replace "collective communication" 
with "collective operation"

p 50, l 31: "using normal point-to-point" is not accurate/sufficient 
enough => "using nonblocking point-to-point"

p 65, 5.13: The example is good but the current text is bad. It is 
simply not allowed to call NBC in a different order. If a certain 
implementation runs into a deadlock does not matter. This would even be 
on of the better scenarios (i.e. an easy-to-noticeable error). Other 
implementations could complete both bcasts (because it thinks they 
match) but provide the wrong data (i.e. the data from the other bcast or 
even a mixture?) - which is a much harder failure to detect.

p 66, example 5.25: should we add sth like the following at the end?
                     "Note: Using nonblocking collectives can fix such 
problems, see example 5.34."

p 69, l 32: maybe better "However, communicator construction might 
induce overheads and consume resources so that this should be used 

p 70, example 5.31: To me this example is not "per se" illegal. Both 
operations simply don't match - that's fine. However, it is possible to 
extent the example so that the final program is still a valid MPI 
program. Maybe just add sth. like "in this form" or "without additional 
collectives that match".

Best regards,

Christian Siebert, Dipl.-Inf.               Research Associate

            NEC Laboratories Europe, NEC Europe Ltd.
        Rathausallee 10, D-53757 Sankt Augustin, Germany

Phone: +49 (0) 2241 - 92 52 44    Fax: +49 (0) 2241 - 92 52 99

  (Registered Office: 1 Victoria Road, London W3 6BL, 2832014)

More information about the mpiwg-coll mailing list