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 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
Speedup
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 Users Services
high performance
reasonable programmability
Users
on SimMillenium
using tools, including research languages and systems
Services
new functionality provided
“making money” through outside customers