ReMP: Low-Downtime Runtime Model-Parallelism Reconfiguration for LLM Serving

2026-06-17

AI Summary

Current large language model inference systems lack the capability to dynamically adjust model parallelism topologies at runtime, necessitating service restarts under varying workloads and causing multi-minute disruptions, loss of KV cache, and substantial recomputation overhead. This work proposes ReMP, the first framework enabling online elastic reconfiguration of combined tensor and pipeline parallelism. By decoupling topology from execution state, designing a two-dimensional KV cache migration mechanism, and orchestrating an end-to-end reconfiguration pipeline, ReMP reduces topology switching latency to 1–7 seconds across 7B–70B models—orders of magnitude faster than restarting. This significantly improves time-to-first-token (TTFT), time per output token (TPOT), and throughput under dynamic workloads.

Abstract

Current large language model (LLM) inference systems universally deploy ultra-large-scale models using a combination of Tensor Parallelism (TP) and Pipeline Parallelism (PP). However, existing systems treat the model parallelism topology as a static configuration that cannot be flexibly adjusted at runtime. This rigid design creates a fundamental contradiction with the dynamically changing inference workloads in real-world scenarios. State-of-the-art systems lack online reconfiguration capabilities and can only switch configurations by restarting the service, resulting in several minutes of service interruption, KV cache loss, and prohibitive recomputation overhead. To address this problem, this paper presents ReMP, a runtime model parallelism reconfiguration framework that supports low downtime. ReMP achieves dynamic adjustment through three key techniques: (1) decoupling the model parallelism topology from runtime state to avoid full service reconstruction; (2) designing a two-dimensional KV cache migration mechanism to preserve reusable cache states after TP/PP changes; and (3) implementing end-to-end online reconfiguration. Experiments demonstrate that ReMP can complete most topology switches within 1-7 seconds on models ranging from 7B to 70B parameters, achieving speedups of tens to over a hundred times compared to the restart approach. Moreover, ReMP significantly outperforms fixed configurations under dynamic workloads, delivering superior performance in terms of TTFT, TPOT, and output throughput.

Problem

• Model Parallelism
• Runtime Reconfiguration
• LLM Serving
• Downtime
• KV Cache

Innovation

• Runtime Reconfiguration
• Model Parallelism
• KV Cache Migration
• Low-Downtime Serving
• LLM Inference