On Wednesday 20 May 2009, Rolf Vandevaart wrote: ... > If I am understanding what is happening, it looks like the original > MPI_Alltoall made use of three algorithms. (You can look in > coll_tuned_decision_fixed.c) > > If message size < 200 or communicator size > 12 > bruck > else if message size < 3000 > basic linear > else > pairwise > end
And 3000 was the observed threshold for bad behaviour so it seems very likely that "basic linear" was the culprit. My testing would suggest that "pairwise" was a good choice for ~3000 (but maybe bruck, as configured by Pavel, is good too). /Peter > With the file Pavel has provided things have changed to the following. > (maybe someone can confirm) > > If message size < 8192 > bruck > else > pairwise > end > > Rolf
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