George Bosilca <bosi...@icl.utk.edu> writes: > Matthieu, > > If you are talking about how Open MPI selects between different broadcast > algorithms you might want to read [1]. We have implemented a dozen > different broadcast algorithms and have run a set of tests to measure their > performance.
I'd been meaning to ask about this sort of thing as I didn't anything written about it. It seems the measurements on which at collective parameter defaults are based were originally from interconnects with at least an order of magnitude difference in performance from typical current ones, and maybe different topology. Have parameters been revisited since, or is it clear they'll still be valid for, say, FDR IB? I know a case that was changed a while ago, but the new alltoallv default algorithm hurt performance on typical chemistry code that might constitute the majority of its use, and it wasn't clear why the change was made. I assume it could be useful to know how things were derived to indicate when it might be worth trying different values as it often seems worthwhile to do so.
