The HPC community is embracing the advantages of mixed-language development environments, presenting challenges for debugging and testing when application execution and data flow cross languages. How can we take advantage of the unique features offered by different languages while minimizing the impact on bug reproduction, root-cause analysis, and solution? This presentation walks through the current mixed-language HPC landscape to describe the problems with testing these types of applications and best-practice solutions using TotalView for HPC. You will learn how these architectures make it easy to “steer” computation between modules of different languages, to accelerate prototyping and development, and how advanced testing techniques provide visibility into the call stack and data for efficient debugging.

1. 1© 2017 Rogue Wave Software, Inc. All Rights Reserved. 1
Approaches to
debugging mixed-
language HPC apps
Exhibitor Forum
SC17

2. 2© 2017 Rogue Wave Software, Inc. All Rights Reserved. 2
Data modeling is critical for machine learning
• Data scientists iterate over huge datasets
• Legacy algorithms are critical
• Most popular languages
– R in scientific communities
– Python in engineering
• Focusing on Python
• Developers use it because
– Ease of use
– Clean syntax
– Extension libraries (many in C/C++)

3. 3© 2017 Rogue Wave Software, Inc. All Rights Reserved. 3
Calling C/C++ from Python
• High performance libraries are written in C/C++ and Fortran
– Run faster
– Rewriting doesn’t make sense
– Advanced multi-threaded capabilities
• Fortunately there are many ways to call between the languages

4. 4© 2017 Rogue Wave Software, Inc. All Rights Reserved. 4
Debugging multiple languages
• Debugging one language is difficult enough
– Especially with many threads/processes
• The language intersection is tougher
– Data comparison
– Glue code
• Issues are:
– Viewing data across language barriers
– Combined call stack
– Extraneous stack frames

5. 5© 2017 Rogue Wave Software, Inc. All Rights Reserved. 5
Python Session Editor
Glue
code
Debugging Python Interpreter

6. 6© 2017 Rogue Wave Software, Inc. All Rights Reserved. 6
Stopped in C/C++ Python Extension
Shows Python & C++

7. 7© 2017 Rogue Wave Software, Inc. All Rights Reserved. 7
Stopped in C/C++ Python Extension
Shows Python & C++

8. 8© 2017 Rogue Wave Software, Inc. All Rights Reserved. 8
Selected Python frame
C++
data
Python
Data

9. 9© 2017 Rogue Wave Software, Inc. All Rights Reserved. 9
Data View
C++
data
Python
Data

10. 10© 2017 Rogue Wave Software, Inc. All Rights Reserved. 10
Numpy

11. 11© 2017 Rogue Wave Software, Inc. All Rights Reserved. 11
Python without filtering
Glue
code
No viewing of Python data and code

12. 12© 2017 Rogue Wave Software, Inc. All Rights Reserved. 12
Python support in TotalView
• Designed for where Python calls C/C++ or vice versa
• Glue frames hidden from view
– Supported for SWIG
– User customizable
• Python information shown
– Code
– Data

13. 13© 2017 Rogue Wave Software, Inc. All Rights Reserved. 13
Stack transformation facility
• Hides stack frames
• Transforms stack frames
• Backbone for:
– Python support
• Useful for any stack frames you want to hide
– Language differences
– Wrapper code

14. 14© 2017 Rogue Wave Software, Inc. All Rights Reserved. 14
Demo

15. 15© 2017 Rogue Wave Software, Inc. All Rights Reserved. 15
Few use cases
• Currently used with large scientific application at Lawrence
Livermore National Laboratory
• Helpful while learning or extending packages such as TensorFlow.

16. 16© 2017 Rogue Wave Software, Inc. All Rights Reserved. 16
TensorFlow basics
• Open source
• Numerical computation
• Usage in machine learning
• Written in C++
– Called from Python

17. 17© 2017 Rogue Wave Software, Inc. All Rights Reserved. 17
TensorFlow
Multithreaded application
Glue code removed
Added a rule for some wrappers

18. 18© 2017 Rogue Wave Software, Inc. All Rights Reserved. 18
How does Rogue Wave help HPC?
TotalView debugger
• Troubleshooting and analysis tool
• Visibility into applications
• Control over applications
• Integrated Reverse Debugging
MemoryScape debugger
• Malloc API misuse
• Memory leaks
• Buffer overflows
• Invalid Read/Write

19. 19© 2017 Rogue Wave Software, Inc. All Rights Reserved. 19
TotalView for HPC
• Comprehensive multi-core and multi-threaded analysis and debug environment
– Thread specific breakpoints
– Control individual thread execution
– View thread specific stack and data
– View complex data types easily
• Integrated Reverse debugging
• Mixed Language - Python C/C++
• Track memory leaks in running applications
• Supports C/C++ on Linux
• Active development for 30+ years
• Allowing the business to have
– Predictable development schedules
– Less time spent debugging

20. 20© 2017 Rogue Wave Software, Inc. All Rights Reserved. 20
Summary
• Comments and questions
• Come see a live demo and learn more at our SC17 booth 1715
• For more information
– https://www.roguewave.com
– White Paper - https://www.roguewave.com/resources/white-
papers/mixed-language-debugging-python-c-cplusplus
– Videos - https://www.youtube.com/watch?v=LXSSstUdKnc
– Evaluation - https://www.roguewave.com/products-services/request-
evaluation

21. 21© 2017 Rogue Wave Software, Inc. All Rights Reserved. 21