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Programming Models for SimMillennium

Explore programming challenges in SimMillennium, facilities for research, Titanium project, tools, analyses, status, support for applications, machines, economy, and measuring success. Discover a robust ecosystem for high-performance computing.

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Programming Models for SimMillennium

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  1. Programming Models for SimMillennium Kathy Yelick NSF Infrastructure Site Visit March 2, 1998

  2. Talk Outline • Programming problems in SimMillenium • Overview of software tools • Facilities for research in programming systems • Titanium project

  3. Programming Challenges • Large scale computations • Optimized simulation algorithms are complex • Use of hierarchical parallel machine • Constructing services must be simple • Cost-conscious programming Minimization algorithms Unstructured meshes ? Adaptive meshes

  4. Infrastructure for Programming Systems • High end machines converging on CLUMPs • Network bandwidth needed for applications • Many non-local accesses (20-50% of grid points for AMR) • Few floating point operations per element • Having machine in the building • provides low-threshold access to hardware • Access to visualization facility crucial • observations in applications • debugging

  5. Programming Tools for SimMillennium • Basic tools installed and supported • 1 Billion bytes of code in the “software warehouse” exported • MPI, C/C++/Fortran compilers, threads, numerical libraries • Novel systems based on user demand • Parallel Matlab, Khoros, HPF, DOE2000 Tools (Petsc, etc.) • Research systems developed here • Communication substrates: • Active Messages (Culler) • Languages: • Split-C (Culler & Yelick) • Titanium(Aiken, Graham, Hilfinger, Yelick) • Service building tools (Brewer, Culler, and Joseph)

  6. Titanium Approach • Performance is primary goal, expressiveness second • Parallelism model • SPMD • Global address space with global/local distinction • Based on safe language: Java • Safety simplifies programming and compiler analysis • Multidimensional arrays added • Immutable classes added • Optimizing compiler • Domain-specific language extensions

  7. New Compiler Analyses for Parallelism • Analysis of synchronization • finds unmatched barriers, parallel code blocks • extends traditional control flow analysis • Analysis of communication • reorder and pipeline memory operations without observed effect • extends traditional dependence analysis • Analyses extended to domain-specific constructs • arrays indexed by domains of points • looping constructs provide summarize information

  8. Titanium Status Speedup • Runs on NOW and SMPs • Sequential performance competitive with C/F77 • preliminary optimizations • within 40% for many problems • 3D multigrid 13% faster on Pentium • Parallel efficiency good • EM3D (unstructured kernel) • 3D AMR limited by algorithm Number of processors

  9. Support for SimMillennium Applications • Long-standing collaboration in fluids and AMR • astrophysics (McKee), combustion (Colella), turbulence (Marcus),… • Planned collaborations in unstructured meshes and sparse solvers • earthquake modeling (Fenves), TCAD (Neureuther),... • Proposed solution: extend Titanium • Linguistic support for unstructured data • Development of new analyses optimization

  10. SimMillenium Machines • CLUMPs adds new level in hierarchy • algorithms currently optimize for caches on SMPs • communication optimizations for distributed memories • need to simultaneously optimize both • Need for Multiprotocol communication • Active Messages and MPI • Eliminating protocols during compilation • Locality and load balance trade-off • understood for flat machine models • different within and between SMPs

  11. Programming in the Economy • New optimization criterion: cost • Mapping performance data to cost models • Use of performance models in algorithm and system design is a common theme of UCB research • Need tools to map performance measurements to these models • Building services • Need to lower the threshold • Service building packages provides functionality, but too low level • Titanium language provides easy integration

  12. Measuring Success • Complete research agendas • high performance • reasonable programmability • Users • on SimMillenium • using tools, including research languages and systems • Services • new functionality provided • “making money” through outside customers

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