Dave, You are absolutely right, the parameters are now 6-7 years old, gathered on interconnects long gone. Moreover, several discussions in this mailing list indicated that they do not match current network capabilities.
I have recently reshuffled the tuned module to move all the algorithms in the base and therefore make them available to other collective modules (the code is available in master and 1.10 and the future 2.0). This move has the potential for allowing different decision schemes to coexists, and be dynamically selected at runtime based on network properties, network topology, or even applications needs. I continue to have hopes that network vendors will eventually get interested in tailoring the collective selection to match their network capabilities, and provide their users with a performance boost by allowing for network specific algorithm selection. George. > On Apr 22, 2016, at 12:02 , Dave Love <d.l...@liverpool.ac.uk> wrote: > > 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. > _______________________________________________ > users mailing list > us...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/users > Link to this post: > http://www.open-mpi.org/community/lists/users/2016/04/28995.php
