Torsten, What does libNBC do in this case? Rajeev

-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Torsten Hoefler Sent: Saturday, August 01, 2009 10:46 AM To: MPI-3 Collective Subgroup Discussions Subject: Re: [mpi3-coll] array parameters in nonblocking collectives

Hello Bin, thanks for bringing this up Bin, it seems like an important issue.

I can see both sides. In general, I would say that all vector collectives are not scalable anyway because they require \Theta(P) memory per node and \Theta(P^2) total. Shifting this by a constant factor probably doesn't matter too much for asymptotic (large-scale) analysis. However, there is certainly a border-zone where something could be gained with transferring the ownership of the arrays.

We will certainly discuss this issue in Helsinki and at the next telecon!

For the future, I would generally expect that, at large scale, such communications are rather sparse. So we should either talk about a sparse interface to vector collectives or its static variant, the graph topology collectives. Those options will also be discussed asap. Both options would potentially reduce the total memory consumption (assuming sparse communications) from \Theta(P^2) to O(P) or O(P log(P)) depending on the problem.

All the Best, Torsten

-- bash$ :(){ :|:&};: --------------------- http://www.unixer.de/ ----- Torsten Hoefler | Postdoctoral Fellow Open Systems Lab | Indiana University 150 S. Woodlawn Ave. | Bloomington, IN, 474045, USA Lindley Hall Room 135 | +01 (812) 855-3608 _______________________________________________ mpi3-coll mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-coll