Compiler Requirements and Directions

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Compiler Requirements and Directions

• Rob Meyer

• September 10, 2009

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NAG in 30 Seconds
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Q1. Language support for HPC

• Provocative short answer We arent
• Longer, politically correct answer but were
  working on it
• Standard-compliant Fortran compiler using latest
  standards (2003)
• OpenMP Library for nodes
• MPI-based Library for loosely coupled systems
• No magic wands (really)
• Managing communications is the key to scalability
• PGAS languages and other vendor libraries/tools
  will help but
• application design (for communications) and
  data distribution will have a profound impact on
  scalability
• MPI, hard as it is, survives for a reason
• If this was easy wed be playing golf (or hanging
  out in the pub)

But co-arrays will be part of Fortran 2008
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Q2. Performance Optimization

• Provocative short answer We arent (again)
• Longer, politically correct answer Were
  (still) working on it
• Inter-process communication is still the critical
  issue
• Hardware providers keep communication costs low
• Programmers reduce communications
• Dynamic optimization?
• Potentially helpful along with a range of other
  techniques
• Hardware-resource-aware middleware?
• Ultimately, massively parallel performance will
  still depend more on the programmer than the
  compiler

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Q3. Support for Heterogeneous cores?

• A series of partial answers
• OpenMP support for conventional cores
• Linking to GPUs for appropriate code
• Have built/tested equivalent routines for GPUs
• Rhetorical question what if we are successful?
• Portability of code?
• Complexity of code?
• Correctness of results?

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Q4. Tools for serial code/parallel novices?

• Not likely (that well do it)
• Not likely to be successful in a broad, sustained
  fashion
• Would we be better off using a community of
  experts to parallelize code and training the
  owners rather than trying to develop HPC for
  Dummies tools?

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Q5 Support of pre-compiled libraries?

• Our own
• Expanding the number of routines optimized for
  multi/many core
• Link to Intel, AMD, etc vendor libraries from our
  code where they have optimized for multi-core
• Identifying options for updating/re-inventing
  MPI-based library

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Some last thoughts

• The landscape is getting more (not less) complex
• Threading tools
• Languages
• Processor options
• Another view If our objective is to produce more
  useful results in a given amount of time given
• Hardware languages
• User software
• User expertise
• Vendor/community software tools
• Vendor/community people expertise?
• Are we putting too much emphasis on compilers and
  tools?
• Should we put more emphasis on training
  supporting users