A Team-Based Methodology of Memory Hierarchy-Aware Runtime Support in Coarray Fortran

Abstract

We describe how 2-level memory hierarchies can be exploited to optimize the implementation of teams in the parallel facet of the upcoming Fortran 2015 standard. We focus on reducing the cost associated with moving data within a computing node and between nodes, finding that this distinction is of key importance when looking at performance issues. We introduce a new hardware-aware approach for PGAS, to be used within a runtime system, to optimize the communications in the virtual topologies and clusters that are binding different teams together. We have applied, and implemented into the CAF OpenUH compiler, this methodology to three important collective operations, namely barrier, all-to-all reduction and one-to-all broadcast, this is the first Fortran compiler that both provides teams and handles such a memory hierarchy methodology within teams.