[1/N] Update doc of Pipeline Parallelism

[ShangmingCai]

Motivation

An explanation of pr #11852

Modifications

Accuracy Tests

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.
• Work with maintainers to merge your PR. See the PR Merge Process

[gemini-code-assist]

Summary of Changes

Hello @ShangmingCai, 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!

This pull request significantly enhances the documentation for Pipeline Parallelism in SGLang. It introduces detailed explanations of recent improvements, including the adoption of asynchronous communication for better efficiency and the novel "Dynamic Chunking" mechanism. This mechanism is designed to optimize the processing of long-context inputs by intelligently adjusting chunk sizes to mitigate pipeline bubbles, thereby improving overall performance and scalability.

Highlights

• New Documentation for Pipeline Parallelism: A new documentation page pipeline_parallelism.md has been added, detailing the concepts and implementation of Pipeline Parallelism in SGLang.
• Async Communication Refactoring: The documentation highlights a refactoring of Pipeline Parallelism to utilize asynchronous communication, aiming to reduce "PP bubbles" and improve efficiency.
• Dynamic Chunking Introduction: The PR introduces and explains "Dynamic Chunking," a new mechanism designed to dynamically adjust chunk sizes during prefill to minimize pipeline bubbles caused by non-uniform model running times, especially for long-context inputs.
• SGLANG_DYNAMIC_CHUNKING_SMOOTH_FACTOR Parameter: A new parameter, SGLANG_DYNAMIC_CHUNKING_SMOOTH_FACTOR, is documented, which controls the smoothing behavior of the dynamic chunking algorithm.

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[gemini-code-assist]

Code Review

This pull request introduces documentation for Pipeline Parallelism, explaining its benefits, implementation details regarding asynchronous communication, and the new dynamic chunking mechanism. The changes are clear and provide a good overview of the feature. I've provided some suggestions to improve clarity, consistency, and fix minor typos in the new documentation file.

[ShangmingCai]

/tag-and-rerun-ci

[ShangmingCai]

More doc about PP will be updated. Will deliver it next week.