Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session X11: Invited Session: New Computational Techniques for Astrophysics |
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Sponsoring Units: DCOMP DAP Chair: Pedro Marronetti, National Science Foundation Room: Oglethorpe Auditorium |
Tuesday, April 8, 2014 10:45AM - 11:21AM |
X11.00001: Porting Legacy LQCD Applicatons to GPUs Invited Speaker: M.A. Clark The exponential growth of floating point power in GPUs, combined with high memory bandwidth, has given rise to an attractive platform upon which to deploy HPC applications. When it comes to legacy applications there is a danger that entire codebases have to be rewritten to fully embrace this computational power. In this session we discuss how to efficiently port legacy lattice quantum chromodynamics (LQCD) applications, e.g., MILC and Chroma, onto GPUs avoiding this rewriting overhead. The approach taken is a community-wide library (QUDA) which provides high-performance implementations for the time-critical LQCD algorithms, which can be linked into any legacy lattice QCD application, providing instant GPU acceleration. We discuss some of the bleeding-edge strategies taken by QUDA to maximize performance, including the use of communication reducing algorithms, mixed-precision methods and an aggressive auto-tuning methodology. While algorithms and routines that are not offloaded to QUDA will typically not be time-critical, they can potentially limit the overall speedup due to the onset of Amdahl's law. We discuss various compile-and-run strategies to circumvent this, including the use OpenACC directives or retargeting the underlying domain-specific language (DSL) to generate GPU code directly from the original source. [Preview Abstract] |
Tuesday, April 8, 2014 11:21AM - 11:57AM |
X11.00002: HACCing the Universe Invited Speaker: Adrian Pope Simulations of large-scale structure formation that can simultaneously encompass a representative volume of the universe and resolve the dark matter halos that host galaxies are required for both planning and analyzing current and future astronomical surveys of galaxies across the sky. In order to harness the power of modern supercomputing systems for running such simulations we have developed the Hardware/Hybrid Cosmology Code (HACC) to address the issues of massive concurrency and heterogeneity. HACC uses n-body methods and splits the calculation of the gravitational force into a long-range component that is highly portable and a short-range component that is tuned to specific compute node architectures. We have developed and used variants of HACC for x86, IBM Cell (LANL/Roadrunner), IBM Blue Gene (ANL/Mira), and GPGPU (ORNL/Titan) systems. This talk will focus on how our experiences with various memory hierarchies and potential performance bottlenecks has influenced our iterations of code design in order to achieve better load-balancing and higher performance. [Preview Abstract] |
Tuesday, April 8, 2014 11:57AM - 12:33PM |
X11.00003: Chemora: A Scalable PDE Solving Framework for Modern HPC Architectures Invited Speaker: Erik Schnetter Modern HPC architectures consist of heterogeneous multi-core many-node systems with deep memory hierarchies. Modern applications continue to employ advanced discretisation methods to study multi-physics problems. Developing such applications that explore cutting-edge physics on cutting-edge HPC systems has become a complex task that requires significant HPC knowledge and experience.\newline Chemora is a generic framework for solving systems of Partial Differential Equations (PDEs) that targets modern HPC architectures. Chemora is based on Cactus, which sees prominent usage in the general relativistic astrophysics community. PDEs are expressed either in a high-level latex-like language or in Mathematica. Discretisation stencils are defined separately from equations, and discretisation can include Finite Differences, Discontinuous Galerkin Finite Elements, Adaptive Mesh Refinement (AMR), and multi-block systems.\newline We use Chemora in the Einstein Toolkit to implement the Einstein Equations on CPUs and on accelerators, and study astrophysical systems such as black hole binaries, neutron stars, and core-collapse supernovae. [Preview Abstract] |
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