Simulation at NASA for the Space Radiation Effort

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Simulation at NASA for the Space Radiation Effort

• Dr. Robert C. Singleterry Jr.
• NASA Administrator's Fellow (Cohort 6)
• NASA Langley Research Center
• HPC Users Forum, Stuttgart, GM

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Overview

• Simulation at NASA for Space Radiation
• What are Our problems?
• Am I (we) Unique?
• Possible Solutions?
• No Real Conclusion!

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Simulation at NASA for Space Radiation

• What is Space Radiation?
• One of the top 5 problems that must be solved for
  extended space travel

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Simulation at NASA for Space Radiation

• Just solve the Boltzmann Equations
• Easy as pie theres pie?

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Simulation at NASA for Space Radiation

• Not so Easy!!
• Stochastic Methods
• Monte Carlo is the most prevalent
• Deterministic Methods
• Discrete ordinates is the most prevalent
• Now can use finite elements for the geometry
  solution
• Straight ahead method (what we use now)
• Dozens if not hundreds of other methods exists
  also
• Possible solutions for space radiation?
• Physics allows the straight ahead method
• Many ways to even solve with this method
• Interpolation
• Ray-by-ray

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Simulation at NASA for Space Radiation

• Todays method of choice for us

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What are Our Problems?

• As vendors move towards a multi/many core
  environment, the individual cores slow down to
  beat thermal limits
• The NASA Space Radiation code is a physics
  research code with a web based front end
• Last thing thought about was execution time
• Physics code was written from 1970 to present
• Legacy does not begin to explain it
• It is serial!!! (We have added dynamic memory
  allocation)
• All is not lost, just limited

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What are Our Problems?

• Interpolation not much to do here
• Thread the mathematics
• Course parallel over interpolation points
• Ray-by-Ray
• Since the rays are independent, each ray can go
  on a core
• Thread the mathematics
• Still hit a wall at about 1000-2000 cores
• Would take more money than we have to rewrite our
  code for a cluster environment
• Latest NASA machine 43,008 cores!!!

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What are Our Problems?

• As cores go from 43,008 to 1,000,000
• Our algorithm is stuck at 1000-2000 cores without
  major rework that we cannot afford
• Not sure how many more cores we could utilize if
  we could afford a rework but ltlt 1,000,000!!!
• -------------- SUMMARY -------------
• As the cores get slower, our execution time gets
  longer as we cannot use more cores
• Yet users want more and better answers as
  computers get more powerful
• OK, as users needs become more demanding

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What are Our Problems?

• HPCWire, 9/24/08, Intel CPUs Will Prevail Over
  Accelerators in HPC
• What we're finding is that if someone is going
  to go to the effort of optimizing an application
  to take advantage of an offload engine, whatever
  it may be, the first thing they have to do is
  parallelize their code
• Richard Dracott, General Manager, HPC Business
  Unit

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Am I (we) Unique?

• There are many small and large ISVs
• Abaqus lt 128 cores
• Few open source packages can gtgt128 cores
• Most (if not all) engineering, day-to-day
  packages cannot use more than 1000 cores
• MCNPX can use lt2000-4000 cores for certain types
  of problems
• Most everybody needs help!
• Those that do not need help can afford
• To rewrite code when new architectures arrive
• To write code from scratch to fit an architecture

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Possible Solutions?

• Smarter compilers Users Point of View!
• No new language, just amend Fortran and C
• Like MP but with MPI Programming Environment
• Nice if housed in current environments
• Intel
• PGI
• Absoft
• etc
• Do not care if production compile takes days
• Enable non-x86 hardware in current compilers
• ASICs
• GPGPU/Cell
• FPGA
• etc

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No Real Conclusions

• Nothing but the possible solutions
• Develop new algorithms to solve the Boltzmann
  Equation so gt1,000,000 cores can be utilized
• Over 10M and 3 years to parallelize and VV what
  we already have and must be done first!!
• Over 100M and 10 years to develop new methods of
  solution to fit the vision of chip makers and
  then VV the methods
• Space Radiation is a small but unique solution
  domain of the total radiation analysis world