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Supercomputing Challenges at the National Center for Atmospheric Research

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  1. Supercomputing Challenges at the National Center for Atmospheric Research Dr. Richard Loft Computational Science Section Scientific Computing Division National Center for Atmospheric Research Boulder, CO USA

  2. Talk Outline • Supercomputing Trends and Constraints • Observed NCAR Cluster Performance (Aggregate) • Microprocessor efficiency: what is possible? • Microprocessor efficiency: recent efforts to improve CAM2 performance. • Some RISC/Vector Cluster Comparisons • Conclusions

  3. The Demand: High Cost of Science Goals • Climate scientists project a need for 150x more computing power of the next 5 years. • T42->T85. Doubling horizontal resolution increases computational cost eightfold. • Many additional constituents will be advected. • New physics: computational cost of CAM/CCM, holding resolution constant, has increased 4x since 1996. More coming… • Future: introducing super-parameterizations of moist processes would increase physics costs dramatically.

  4. Existing Infrastructure Limits at NCAR • Cooling Capacity • 450 tons (1.58 megawatts) • Most limiting • One P690 node ~ 7.9 KW ~ 2.5 tons • Balance cooling with power • Power ~ 1.2 MW without modifications • Second most limiting • Currently NCAR computer room draws 602 KW • About 400 kw from IBM clusters • Space ~ 14,000 sq.ft. • P690 ~ 196 W/sq. ft. • Least limiting based on current trends

  5. Mass Storage Growth • 1.3 Pbytes total • Adding ~3 Tbytes/day • 5 year doubling times - • Unique files: 2.1 years • File size: 10.4 years • Media performance (GB/$) 1.9 years • Alarming trends • MSS growth rate doubling time has accelerated over past year. Now 18 months. • MSS costs are increasing…

  6. Observed Cluster Performance (Aggregate)

  7. IBM Clusters at NCAR • Bluesky: 1024 IBM 1.3 GHz Power-4 cluster • 32 P690/32 compute servers • 736 in 92, 8 way “nodes” (bluesky8) • 288 in 9, 32 way “nodes” (bluesky32) • Peak: 5.234 TFlops • Dual “Colony” interconnect • Blackforest: IBM 375 MHz Power-3 cluster • 283 “winterhawk” 4-way SMP’s • Peak: 1.698 TFlops • TBMX interconnect

  8. Observed IBM Cluster Efficiencies • Newer systems are less efficient. • Larger nodes are more efficient. • Max sustained performance: 320.3 GFlops

  9. Why is workload efficiency low? • Computational character of workload average: • L3 cache miss rate 31% • computational intensity is 0.8 • Applications are memory bandwidth limited. • Simple BW model predicts 5.5% for bluesky32. • A good metric of efficiency is Flop/cycle. • Factors out dual FPU’s. • Bluesky32: 0.18 Flop/cycle • Blackforest: 0.23 Flop/cycle

  10. RISC Cluster Network Comparison • IBM Power-4 cluster with dual “Colony” network. • IBM Power-3 cluster with single TBMX network. • Compaq Alpha cluster with Quadrix network. • Bisection Bandwidth • Important for global communications • XPAIR benchmark initiates all to all communication. • Dual Colony P690 local:global BW ratio 50:1 • Global Reductions • For P processors these should scale as log(P). • Actually scales linearly.

  11. Cluster Network Performance

  12. Microprocessor efficiency: What is possible?

  13. Example: 3-D FFTPerformance • Hand tuned multithreaded, 3-D FFT (STK) • Three 1-D FFT on each axis with transpositions • FFTs are memory bandwidth intensive • Both loads and Flop’s scale like N*log(N) • The FFT is not multiply-add dominated • The FFT butterfly is a non local, strided calculation. • Gets more non local as size of FFT increases • 1024^3 Transforms on P690 (IBM Power-4)

  14. Microprocessor efficiency: Recent efforts to improve CAM2 performance…

  15. CCM Benchmark Performance on Existing Multiprocessor Clusters

  16. Some RISC/Vector Cluster Comparisons…

  17. Processor Comparison

  18. IBM P690 Cluster • 5.3 TFlops peak • 1024 processors (32, 32 way P690 nodes) • 5.2 Gflops/processor • Observed 4.1-4.5% of peak on NCAR codes • Max sustained on workload: 213.5 GFlops • Est. Peak Price Performance: $2.6/MFlops • Sustained Price Performance: $59/MFlops • Sustained Power Performance: 0.7 Gflops/KW

  19. Earth Simulator • 40.96 Tflops peak • 5120 Processors (640, 8 processor GS40 nodes) • 8 Gflops/processor • Estimate 30% of peak on NCAR codes • Est. Max sustained on workload: 12,200 GFlops • Est. Peak Price Performance: $8.5/MFlops • Est. Sustained Price Performance: $28/MFlops • Est. Sustained Power Performance: 1.525 Gflops/KW

  20. Power 4 die floor plan

  21. Power 4 cache/CPU area comparison

  22. Conclusions • Infrastructure (power, cooling, space) are becoming critical constraints. • NCAR IBM clusters sustain 4.1%-4.5% of peak. • Workload is memory bandwidth limited. • RISC cluster interconnects are not great. • We’re making steady progress learning how to program around these limitations. • At this point, vector systems appear to be about 2x more cost effective in both price and power performance.

  23. Pentium-4 die floor plan

  24. Pentium-4 cache/CPU comparison

  25. Itanium II die floor plan

  26. Itanium II CPU/cache area comparison