Load-balancing scatter operations for Grid computing

We present solutions to statically load-balance scatter operations in parallel codes run on Grids. Our load-balancing strategy is based on the modification of the data distributions used in scatter operations. We need to modify the user source code, but we want to keep the code as close as possible to the original. We study the replacement of scatter operations with a parameterized scatter, allowing a custom distribution of data. The paper presents: (1) a general algorithm which finds an optimal distribution of data across processors; (2) a quicker guaranteed heuristic relying on hypotheses on communications and computations; (3) a policy on the ordering of the processors. Experimental results with an MPI scientific code of seismic tomography illustrate the benefits obtained from our load-balancing.