[WIP][V1][P/D]Enhance Performance for P2pNcclConnector

[Abatom]

Enhance Performance for P2pNcclConnector

• Support asynchronous loading of KV cache
• Release KV cache after sending is completed

[gemini-code-assist]

Summary of Changes

Hello @Abatom, 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 focuses on enhancing the performance and robustness of the P2pNcclConnector by transitioning key KV cache transfer operations to an asynchronous model. It introduces non-blocking mechanisms for sending and receiving KV cache data and implements a more precise way to track the completion of these transfers, which is crucial for efficient resource management and timely KV cache release. Additionally, the changes improve the reliability of the service discovery component by adding liveness tracking for prefill and decode instances.

Highlights

• Asynchronous KV Cache Operations: Removed blocking waits for KV cache saving and sending, and made KV cache reception non-blocking. This allows for more efficient overlapping of computation and communication, directly enhancing performance.
• KV Cache Transfer Completion Tracking: Implemented a more robust mechanism within the P2pNcclEngine to track the completion of KV cache transfers (both sending and receiving) for each request. A request's KV cache is now considered fully transferred only when all layers have been processed, enabling timely resource release.
• Service Discovery Liveness Tracking: Introduced a liveness tracking and cleanup mechanism for prefill and decode instances in the service discovery proxy. Instances are now associated with a timestamp and stale entries are periodically removed, improving system robustness and ensuring requests are routed to active instances.

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[gemini-code-assist]

Code Review

This pull request introduces significant performance enhancements for the P2pNcclConnector by implementing asynchronous KV cache loading and improving the release mechanism. The changes include a new instance heartbeat system in the proxy, non-blocking tensor reception, and refined completion tracking for KV cache transfers. While the overall direction aligns with the stated objectives, a critical logical issue was identified in p2p_nccl_connector.py regarding the condition for adding requests to _requests_need_load, which could impact the correctness of KV cache loading. Additionally, a type safety violation in p2p_nccl_engine.py where recv_tensor might return None despite being typed for torch.Tensor should be addressed. Minor improvements in logging practices and type hints are also suggested.

[github-actions]

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