If you can avoid them it is better to avoid them. However it is always
better to use a MPI_Alltoall than coding your own all to all with
point to point, and in some algorithms you *need* to make a all to all
communication. What you should understand by "avoid all to all" is not
avoid MPI_alltoall, but choose a mathematic algorithm that does not
need all to all.
The algorithmic complexity of AllReduce is the same as AlltoAll.
Aurelien
Le 12 mars 08 à 17:01, Brock Palen a écrit :
I have always been told that calls like MPI_Barrior() MPI_Allreduce()
and MPI_Alltoall() should be avoided.
I understand MPI_Alltoall() as it goes n*(n-1) sends and thus grows
very very quickly. MPI_Barrior() is very latency sensitive and
generally is not needed in most cases I have seen it used.
But why MPI_Allreduce()?
What other functions should generally be avoided?
Sorry this is kinda off topic for the list :-)
Brock Palen
Center for Advanced Computing
bro...@umich.edu
(734)936-1985
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