12715

A Framework for Lattice QCD Calculations on GPUs

F. T. Winter, M. A. Clark, R. G. Edwards, B. Joo
Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
arXiv:1408.5925 [hep-lat], (25 Aug 2014)

@article{2014arXiv1408.5925W,

   author={Winter}, F.~T. and {Clark}, M.~A. and {Edwards}, R.~G. and {Jo{‘o}}, B.},

   title={"{A Framework for Lattice QCD Calculations on GPUs}"},

   journal={ArXiv e-prints},

   archivePrefix={"arXiv"},

   eprint={1408.5925},

   primaryClass={"hep-lat"},

   keywords={High Energy Physics – Lattice, Computer Science – Mathematical Software, Physics – Computational Physics},

   year={2014},

   month={aug},

   adsurl={http://adsabs.harvard.edu/abs/2014arXiv1408.5925W},

   adsnote={Provided by the SAO/NASA Astrophysics Data System}

}

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Computing platforms equipped with accelerators like GPUs have proven to provide great computational power. However, exploiting such platforms for existing scientific applications is not a trivial task. Current GPU programming frameworks such as CUDA C/C++ require low-level programming from the developer in order to achieve high performance code. As a result porting of applications to GPUs is typically limited to time-dominant algorithms and routines, leaving the remainder not accelerated which can open a serious Amdahl’s law issue. The lattice QCD application Chroma allows to explore a different porting strategy. The layered structure of the software architecture logically separates the data-parallel from the application layer. The QCD Data-Parallel software layer provides data types and expressions with stencil-like operations suitable for lattice field theory and Chroma implements algorithms in terms of this high-level interface. Thus by porting the low-level layer one can effectively move the whole application in one swing to a different platform. The QDP-JIT/PTX library, the reimplementation of the low-level layer, provides a framework for lattice QCD calculations for the CUDA architecture. The complete software interface is supported and thus applications can be run unaltered on GPU-based parallel computers. This reimplementation was possible due to the availability of a JIT compiler (part of the NVIDIA Linux kernel driver) which translates an assembly-like language (PTX) to GPU code. The expression template technique is used to build PTX code generators and a software cache manages the GPU memory. This reimplementation allows us to deploy an efficient implementation of the full gauge-generation program with dynamical fermions on large-scale GPU-based machines such as Titan and Blue Waters which accelerates the algorithm by more than an order of magnitude.
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