Our presentation on a repository of logical errors in parallel programs (MPI, OpenMP, CUDA) for teaching code correctness.

1. PRESENTED BY:
Towards Developing a Repository of Logical Errors
Observed in Parallel Code to Teach Code Correctness
EduHPC 2018 workshop @SC18
November 11, 2018
Trung Nguyen Ba: tnguyenba@cs.umass.edu
Ritu Arora: rauta@tacc.utexas.edu

2. Challenges in parallel programming for
beginners
It can be very hard to test and debug
parallel programs
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3. IPT

4. Why ?
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5. Logical error repository
Errors
Internal
Sources
Stack
Overflow
( Students, developers etc.)
Repository
MPI tags
OpenMP
tags
CUDA tags
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6. Examples of the bug and its tag
MPI: Incorrect initialization of variables
Parallel Program (with logical error) Parallel Program (fixed)
int range = 100/size;
int start = rank*range;
int end = start + range;
int sum = 1;
for(int i=start;i < end;i++) {
sum +=1;
}
int recv = 0;
MPI_Allreduce(&sum,&recv,1,MPI_INT
,MPI_SUM, MPI_COMM_WORLD);
sum = recv;
int range = 100/size;
int start = rank*range;
int end = start + range;
int sum = (rank==0)? 1: 0;
for(int i=start;i < end;i++) {
sum +=1;
}
int recv = 0;
MPI_Allreduce(&sum,&recv,1,MPI_INT,
MPI_SUM, MPI_COMM_WORLD);
sum = recv;
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7. Each logical error contains
Buggy version Fixed version
Instructions for compile and run Explanation
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8. How can people use this repository ?
Source code from the github
Quizzes on the logical errors
Logical error reproducibility for experimenting
● https://github.com/ritua2/IPT/tree/master/bug-patterns/Quizzes
● https://github.com/ritua2/IPT/tree/master/bug-patterns
● Instructions on how to recreate the logical errors for learning or
analyses
○ Note: not guaranteed for non-deterministic errors
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9. Example of questions in the quizzes
Text version Online version
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10. Evaluation of our work
Relevance test
Usefulness test
● Will it help people in avoiding the errors in the future by seeing them in the
repository?
● How easy do people miss these errors ?
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11. Command line
API
Web interface
Parallel Programing
Model and Tag
(# errors)
Repository
MPI OpenMP CUDA
MPI
tags
OpenMP
tags
CUDA
tags
User provides
Send to
process
Result returned
Result returned
Web-Enabled Repository of Errors
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12. What next ?
Repository of errors in parallel programs
Database of errors in parallel programs
Error
Internal Sources Stack Overflow
( Students, developers etc.)
Error
Internal Sources Stack Overflow
( Students, developers etc.)
Real-world
projects
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13. Logical error submission
Web Service Submission Format
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14. Conclusion
● We have started building a repository of logical errors for helping
students in learning parallel programming
● Repository usage:
○ Download source code from the repo
○ Use the quizzes
○ Reproduce the bugs
● We are collecting data to evaluate the repository for relevance and
usefulness
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15. Acknowledgement
The work presented in this paper was made possible
through the National Science Foundation (NSF) award
number 1642396.
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16. Thanks!
Any questions, comments, concerns?
Contact:
Ritu Arora: rauta@tacc.utexas.edu
Trung Nguyen Ba: tnguyenba@cs.umass.edu
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