Optimize tuple unpacking in skyrl_gym_generator.generate()

[davenpi]

Hey! 👋🏾

Love what you're building with SkyRL - the modular architecture makes the system level challenges super clear!

I was exploring the codebase and noticed an opportunity to optimize the tuple unpacking in skyrl_gym_generator.py. The current implementation iterates through all_outputs 5 separate times and uses sum() for list concatenation, which has O(n²) complexity.

What I Changed

Replaced the multiple iterations with a single zip(*all_outputs) call to transpose the data in one pass.

Before:

responses = sum([[output[0]] for output in all_outputs], [])
rewards = sum([[output[1]] for output in all_outputs], [])
# ... 3 more similar lines

After:

responses, rewards, stop_reasons, loss_masks, prompt_token_ids = map(list, zip(*all_outputs))

Performance Impact

I wrote a quick benchmark script and the speedup scales nicely with batch size:

• Small batches (10 items): ~5x faster
• Large batches (1000 items): ~50x faster (2.51ms → 0.05ms)

The optimization maintains identical functionality - just more efficient execution. Happy to discuss any questions!

[gemini-code-assist]

Summary of Changes

Hello @davenpi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've submitted a pull request to enhance the performance of the skyrl_gym_generator.py module. The core change involves refactoring the tuple unpacking process within the generate function. Previously, this was handled by multiple inefficient sum() calls, leading to quadratic time complexity for list concatenation. My update replaces this with a single, optimized line utilizing zip(*all_outputs) and map(list, ...), which transposes the data in a single pass. This modification not only simplifies the code but also delivers substantial speed improvements, particularly noticeable with larger data batches.

Highlights

• Performance Optimization: I've optimized the tuple unpacking logic within the generate method of skyrl_gym_generator.py.
• Code Simplification: The previous implementation iterated through all_outputs five separate times and used sum() for list concatenation, which has O(n²) complexity. I've replaced this with a single, more Pythonic line using map(list, zip(*all_outputs)) to transpose the data efficiently.
• Performance Gains: This change yields significant performance improvements, with benchmarks showing a ~5x speedup for small batches and a ~50x speedup for large batches (1000 items), reducing processing time from 2.51ms to 0.05ms.

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[gemini-code-assist]

Code Review

This pull request provides a great performance optimization by replacing an inefficient tuple unpacking method with a more Pythonic and faster approach using zip. My review focuses on an edge case where the new implementation could fail. I've identified that an empty input list would cause a ValueError and have provided a suggestion to handle this case gracefully, making the implementation more robust.

[tyler-griggs]

Hi @davenpi , thanks for your interest in SkyRL! I'm glad you've enjoyed using it and have had a chance to start digging into the codebase.

LGTM