The performance of multi-turn, agentic LLM inference is increasingly dominated by KV-Cache storage I/O rather than computation. In prevalent disaggregated architectures, loading the massive KV-Cache from external storage creates a fundamental imbalance: storage NICs on prefill engines become bandwidth-saturated, while those on decoding engines remain idle. This asymmetry severely constrains overall system throughput.

Although the native RDMA interface allows for high throughput and low latency, its low-level abstraction raises significant programming challenges. Consequently, numerous systems encapsulate the RDMA interface into more user-friendly high-level abstractions such as Socket, MPI, and RPC. However, this ease of development often incurs considerable performance degradation. To address this trade-off, this paper introduces RB2, a high-performance RDMA-based Distributed Ring Buffer (DRB). RB2serves as a middle layer that effectively conceals the low-level details of the RDMA interface while also facilitating extension to other high-level abstractions.Nonetheless, it is non-trivial for DRBs to preserve the RDMA performance. We optimize the performance of RB2in three aspects. First, we perform micro-benchmarks to identify the pointer synchronization methods that are seemingly counter-intuitive but offer optimal performance improvements. Second, we propose an adaptive batching mechanism to alleviate the limitations of conventional fixed batching. Finally, we build an efficient memory subsystem using various optimization techniques. RB2outperforms SOTA designs by achieving 2.5 × to 7.5 × throughput while maintaining comparable tail latency for small messages.