KV Cache Transfer in Disaggregated Serving

In disaggregated serving architectures, KV cache must be transferred between prefill and decode workers. TensorRT-LLM supports two methods for this transfer:

Default Method: NIXL

By default, TensorRT-LLM uses NIXL (NVIDIA Inference Xfer Library) with UCX (Unified Communication X) as backend for KV cache transfer between prefill and decode workers. NIXL is NVIDIA’s high-performance communication library designed for efficient data transfer in distributed GPU environments.

Specify Backends for NIXL

TODO: Add instructions for how to specify different backends for NIXL.

Alternative Method: UCX

TensorRT-LLM can also leverage UCX (Unified Communication X) directly for KV cache transfer between prefill and decode workers. There are two ways to enable UCX as the KV cache transfer backend:

1. Recommended: Set cache_transceiver_config.backend: UCX in your engine configuration YAML file.

2. Alternatively, set the environment variable TRTLLM_USE_UCX_KV_CACHE=1 and configure cache_transceiver_config.backend: DEFAULT in the engine configuration YAML.

This flexibility allows users to choose the most suitable method for their deployment and compatibility requirements.