Approaches to debugging mixed-language HPC apps

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Approaches to
debugging mixed-
language HPC apps
Exhibitor Forum
SC17

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++)

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

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

Python Session Editor
Glue
code
Debugging Python Interpreter

Stopped in C/C++ Python Extension
Shows Python & C++

Selected Python frame
C++
data
Python
Data

Data View
C++
data
Python
Data

Numpy

Python without filtering
Glue
code
No viewing of Python data and code

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

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

Demo

Few use cases
• Currently used with large scientific application at Lawrence
Livermore National Laboratory
• Helpful while learning or extending packages such as TensorFlow.

TensorFlow basics
• Open source
• Numerical computation
• Usage in machine learning
• Written in C++
– Called from Python

TensorFlow
Multithreaded application
Glue code removed
Added a rule for some wrappers

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

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

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

Approaches to debugging mixed-language HPC apps

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