The reverse-acceleration model for programming petascale hybrid systems

  • Authors:

  • S. Pakin;M. Lang;D. J. Kerbyson

  • Affiliations:

  • Los Alamos National Laboratory, Los Alamos, New Mexico;Los Alamos National Laboratory, Los Alamos, New Mexico;Los Alamos National Laboratory, Los Alamos, New Mexico

  • Venue:
  • IBM Journal of Research and Development
  • Year:
  • 2009

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Abstract

Current technology trends favor hybrid architectures, typically with each node in a cluster containing both general-purpose and specialized accelerator processors. The typical model for programming such systems is host-centric: The general-purpose processor orchestrates the computation, offloading performancecritical work to the accelerator, and data are communicated only among general-purpose processors. In this paper, we propose a radically different hybrid-programming approach, which we call the reverse-acceleration model. In this model, the accelerators orchestrate the computation, offloading work that cannot be accelerated to the general-purpose processors. Data is communicated among accelerators, not among general-purpose processors. Our thesis is that the reverse-acceleration model simplifies porting codes to hybrid systems and facilitates performance optimization. We present a case study of a legacy neutron-transport code that we modified to use reverse acceleration and ran across the full 122,400 cores (general-purpose plus accelerator) of the Los Alamos National Laboratory Roadrunner supercomputer. Results indicate a substantial performance improvement over the unaccelerated version of the code.