On Sun, Jul 22, 2012 at 08:30:26PM +0200, Rolf Rabenseifner wrote:
Torsten and Bill,
Torsten:
I would agree to Bill. We should have an info argument allowing the user to state that all displ_units are the same like we have for count :-). A topic for MPI-3.1!
Yes, it is not needed for MPI-3.0, because with two Allreduces with MIN and MAX of disp_unit, all processes know in O(log(p)) whether it is the same value in all processes. Sure, this is trivial but I still like an O(1) (zero communication) info argument better :-).
Bill, yes, here a draft:
Advice to users. If an application should scale to a large number of processes, then it is recommended for scalability reasons that all processes provide the same disp_unit argument on all processes. End of advice to users. I think this does not belong into the standard. If we start those things then we need to add the same for the size and dozens of other "collective" arguments (think compressibility of graphs etc.).
I also think that we're digressing :-). We still didn't decide if the WG likes the displ in the query function or not. Best, Torsten -- ### qreharg rug ebs fv crryF ------------- http://www.unixer.de/ ----- Torsten Hoefler | Performance Modeling and Simulation Lead Blue Waters Directorate | University of Illinois (UIUC) 1205 W Clark Street | Urbana, IL, 61801 NCSA Building | +01 (217) 244-7736