Optimizing Applications and Message-Passing Libraries for the QPACE Architecture

The goal of the QPACE project is to build a novel cost-efficient massive parallel supercomputer optimized for LQCD (Lattice Quantum Chromodynamics) applications. Unlike previous projects which use custom ASICs, this is accomplished by using the general purpose multi-core CPU PowerXCell 8i processor tightly coupled with a custom network processor implemented on a modern FPGA. The heterogeneous architecture of the PowerXCell 8i processor and its core-independent OS-bypassing access to the custom network hardware and application-oriented 3D torus topology pose interesting challenges for the implementation of the applications. This work will describe and evaluate the implementation possibilities of message passing APIs: the more general MPI, and the more QCD-oriented QMP, and their performance in PPE centric or SPE centric scenarios. These results will then be employed to optimize HPL for the QPACE architecture. Finally, the developed approaches and concepts will be briefly discussed regarding their applicability to heterogeneous node/network architectures as is the case in the "High-speed Network Interface with Collective Operation Support for Cell BE (NICOLL)" project