Jeff Squyres (jsquyres) wrote:
>
> Lam obeys mpi's ordering rules, which are quite deterministic in some
> cases and nondeterministic in others.
>
> I know I wrote some text about this in an mpi magazine column a while
> ago, but I unfortunately don't remember which one. See all my
> articles at http://cw.squyres.com (I really need to move these to
> www.open-mpi.org...).
>
Jeff's reply greatly appreciated. Now I hope "page currently
unavailable" will be resolved before I forget about it.
We have found that opportunistic ordering in MPI_Allreduce can break
major applications, depending on data set and willingness to restart and
accept non-repeatable results, unless sum reduction is done with extra
precision, or the applications promote it to double, or even capture
Allreduce internally and process in a QA tested good order. Maybe I'm
dense, but I don't know if this relates to the original question.
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