HACC: Simulating Sky Surveys on State-of-the-Art Supercomputing
  Architectures
  Current and future surveys of large-scale cosmic structure are associated
with a massive and complex datastream to study, characterize, and ultimately
understand the physics behind the two major components of the 'Dark Universe',
dark energy and dark matter. In addition, the surveys also probe primordial
perturbations and carry out fundamental measurements, such as determining the
sum of neutrino masses. Large-scale simulations of structure formation in the
Universe play a critical role in the interpretation of the data and extraction
of the physics of interest. Just as survey instruments continue to grow in size
and complexity, so do the supercomputers that enable these simulations. Here we
report on HACC (Hardware/Hybrid Accelerated Cosmology Code), a recently
developed and evolving cosmology N-body code framework, designed to run
efficiently on diverse computing architectures and to scale to millions of
cores and beyond. HACC can run on all current supercomputer architectures and
supports a variety of programming models and algorithms. It has been
demonstrated at scale on Cell- and GPU-accelerated systems, standard multi-core
node clusters, and Blue Gene systems. HACC's design allows for ease of
portability, and at the same time, high levels of sustained performance on the
fastest supercomputers available. We present a description of the design
philosophy of HACC, the underlying algorithms and code structure, and outline
implementation details for several specific architectures. We show selected
accuracy and performance results from some of the largest high resolution
cosmological simulations so far performed, including benchmarks evolving more
than 3.6 trillion particles.
