QPACE: Energy-Efficient High Performance Computing.

QPACE is a special purpose supercomputer for Lattice Quantum Chromodynamics (LQCD) calculations designed with focus on low power consumption. To open QPACE for a broader range of High Performance Computing (HPC) applications, the High Performance Linpack benchmark (HPL), whose calculations are common for some class of HPC applications, is chosen for porting to the QPACE system. In this respect, this paper discusses features and limitations of the QPACE architecture. It starts with analysing the requirements of HPL and, based on that, presents different approaches to meet these requirements. The paper describes the different stages of porting HPL to QPACE ranging from low-level communication interface to MPI collective operations. Finally, HPL benchmark results show to what extent HPC applications other than LQCD could benefit from QPACE.