2. Implementation of Efficient Check-pointing and Restart on CPU - GPU
Sumanth Suraneni
Sharath Prasad
Harsha Sutaone
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3. Introduction GPU. CPU – GPU systems Checkpoint GPU on CPU-GPU
Restart from checkpoint on CPU
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4. Motivation CPU – GPUs general purpose workloads
Dependability an issue in future GPUs
GPU fault tolerance is a nascent field
Checkpointing implementations on GPUs are at application level
We explore micro-architectural changes to GPUs
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5. Background OpenCL Programming Model Southern Islands Architecture
Multi2Sim CPU-GPU Simulator
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6. OpenCL Programming Model
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7. OpenCL Programming Model
Simplified Mapping of OpenCL onto AMD Accelerated Parallel Processing
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8. OpenCL Programming Model
Work-item Grouping into Work-groups and Wavefronts
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9. Southern Islands Architecture
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10. Southern Islands Architecture
Compute Unit
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11. Southern Islands Architecture
Kernel State
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12. Multi2Sim CPU-GPU Simulator
Software entities defined in the OpenCL Programming Model
An ND-Range is formed of work-groups, which are, in turn, sets of work-items executing the same OpenCl C Kernel code
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13. Multi2Sim CPU-GPU Simulator
Interaction between user code, OS-code, and hardware, comparing native and simulated environments
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14. Multi2Sim CPU-GPU Simulator
Running an OpenCL Kernel on a Southern islands GPU
Block Diagram of a Compute Unit
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15. Implementation SIEmuCreate() SIEmuRun() si_wavefront_execute()
Assign global memory
List running and waiting work-groups
SIEmuRun()
Dequeue & Enqueue running work-groups and waiting work-groups
Work-group create
si_wavefront_execute()
Instruction dump
Next PC = Current PC + Instruction Size
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16. Implementation
Checkpoint Implementation
ND-Range : ID, work dimension, number of VGPRs & SGPRs used
Work-group : ID, work-groups finished, wavefronts completed & at barrier, wavefront count
Wavefront : ID, SREGs, execution state of wavefront, instruction count.
Work-item : ID, VREGs, global memory access size & address
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17. Implementation LDS (Local Data Share) Global memory
LDS module of executing work-group.
All pages are stored.
Global memory
Stored until global memory top.
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18. Implementation Completed Work-groups
Store the list of finished work-groups in a file.
Unexecuted Wavefronts during checkpoint
Store into a separate file while writing the checkpoint file.
Read from the file to start execution during restart.
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19. Implementation
Checkpoint
Checkpoint Trace
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20. Implementation
Restart
Restart Trace
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21. Implementation
Verification Strategy
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22. Evaluation
Workgroups
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23. Evaluation
Instruction Count
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24. Evaluation
Checkpoint Size
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25. Evaluation
LDS Comparison
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26. Bugs Encountered
LDS misalignment.
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27. Bugs Encountered
Unexecuted wave front during checkpoint
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28. Future Scope Further minimization of LDS snapshot
Keeping track of pages modified and storing only those
Implementing a driver call to checkpoint
Hardware Complexity of the implementation
Compression algorithms during multiple checkpoints
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29. THANK YOU
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