RDMA has been widely adopted for high-speed datacenter networks. However, native RDMA merely supports one-to-one reliable connection, which mismatches various applications with group communication patterns (e.g., one-to-many). While there are some multicast enhancements to address it, they all fail to simultaneously achieve optimal multicast forwarding and fully unleash the distinguished RDMA capabilities. In this paper, we present Gleam, an RDMA-accelerated multicast protocol that simultaneously supports optimal multicast forwarding, efficient utilization of the prominent RDMA capabilities, and compatibility with the commodity RNICs. At its core, Gleam re-purposes the existing RDMA RC logic with careful switch coordination as an efficient multicast transport. Gleam performs the one-to-many connection maintenance and many-to-one feedback aggregation, based on an extended multicast forwarding table structure, to achieve integration between standard RC logic and in-fabric multicast. We implement a fully functional Gleam prototype. With extensive testbed experiments and simulations, we demonstrate Gleam's significant improvement in accelerating multicast communication of realistic applications. For instance, Gleam achieves 2.9X lower communication time of an HPC benchmark application and 2.7X higher data replication throughput.

翻译：RDMA已广泛应用于高速数据中心网络。然而，原生RDMA仅支持一对一可靠连接，这与具有组通信模式（例如一对多）的多种应用不匹配。虽然已有一些多播增强方案试图解决该问题，但它们均未能同时实现最优多播转发并充分释放RDMA的独特能力。本文提出Gleam，一种RDMA加速的多播协议，该协议同时支持最优多播转发、高效利用RDMA突出能力以及兼容商用RNIC。其核心思想是通过精心的交换机协调，将现有RDMA RC逻辑重新用作高效的多播传输机制。Gleam基于扩展的多播转发表结构执行一对多连接维护和多对一反馈聚合，从而实现标准RC逻辑与网内多播的融合。我们实现了完整功能的Gleam原型。通过广泛的实验台测试和仿真，我们证明了Gleam在加速实际应用多播通信方面的显著提升。例如，Gleam使某HPC基准测试应用的通信时间降低2.9倍，数据复制吞吐量提升2.7倍。