Lab 09: Interview Scenarios
Annotated code reading lab. Running code is optional.
Interview Scenarios
This lab maps directly to the handbook section. Read the related handbook section first, then use the lab page and starter file to connect the concept to concrete variables, shapes, APIs, and interview-ready explanations.
Interview Scenarios
Practice explaining a parallelism choice with problem, mechanism, communication, tradeoff and measurement.
Mechanism to keep in mind
- `problem` states the bottleneck.
- `mechanism` says what is sharded.
- `measurement` says how to verify.
Annotated Code Preview
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Excerpt from code/lab-09-interview-scenarios/interview_scenarios.md. The linked starter file is the source of truth.
Distributed training scales beyond one device by partitioning data, model state, or computation across ranks. The key questions are what is replicated, what is sharded, which collective runs on the critical path, and how optimizer semantics stay consistent.What each block is doing
- Setup / contract
- `problem` states the bottleneck.
- Main transition
- `mechanism` says what is sharded.
- Interview hook
- `measurement` says how to verify.
Reading checkpoints
- A good answer names the state being moved.
- Tradeoffs are part of the answer.
- Profiler evidence beats framework-name lists.
What this lab prevents
- Do not recite DDP/FSDP/TP/PP without dataflow.
- Do not ignore optimizer state and activation memory.
How to say it out loud
Practice explaining a parallelism choice with problem, mechanism, communication, tradeoff and measurement. Then explain the code by naming the state being transformed, the axis or shape that matters, and the tradeoff that would appear in a real system.
Additional intuition
- Use official docs and papers for API behavior and factual claims; use blogs only to improve the mental picture.
- If support matrices, performance behavior or backend choices are version-sensitive, check current docs before repeating them.
- A strong interview answer names the state object, the shape or axis it changes, and the tradeoff it creates.