From: Tahar Amari (amari_at_cpht.polytechnique.fr)
Date: Sat Feb 14 2009 - 10:37:28 PST
Hello, A naive question : I am trying to understand the manual for some typical application. SUppose that I distribute my data as hared one blocks (it is supposed to be for example a 2D grid with scalar number defined at the center of each cell) Then I perfom some operation that needs information of neighbouring blocs (typically like in finite difference computing a laplacian in each block). This operation will access some values close to the "interface " of the block, so with no "affinity" with the local block. With MPI we need to communicate (send and get) this precise type of needed data , known as "ghost" cells and then perform the operator. with UPC, if I do not do anything special (unlike in MPI) is it possible to do this ? If yes, I guess that UPC will do the communication, and therefore if nothing special tells what data to comunicate, this is where penalty will be big ? Has anyone tested a simple laplacian on a square grid, with simple shared data, and measured how much we loose or not , compared to the method in which one will do almost as much effort as with MPI ? Many thanks Tahar -------------------------------------------- T. Amari Centre de Physique Theorique Ecole Polytechnique 91128 Palaiseau Cedex France tel : 33 1 69 33 42 52 fax: 33 1 69 33 30 08 email: <mailto:[email protected]> URL : http://www.cpht.polytechnique.fr/cpht/amari