RDMA is becoming prevalent because of its low latency, high throughput and low CPU overhead. However, in current datacenters, RDMA remains a single path transport which is prone to failures and falls short to utilize the rich parallel network paths. Unlike previous multi-path approaches, which mainly focus on TCP, this paper presents a multi-path transport for RDMA, i.e. MP-RDMA, which efficiently utilizes the rich network paths in datacenters. MP-RDMA employs three novel techniques to address the challenge of limited RDMA NICs on-chip memory size: 1) a multi-path ACK-clocking mechanism to distribute traffic in a congestion-aware manner without incurring per-path states; 2) an out-of-order aware path selection mechanism to control the level of out-of-order delivered packets, thus minimizes the meta data required to them; 3) a synchronise mechanism to ensure in-order memory update whenever needed. With all these techniques, MP-RDMA only adds 66B to each connection state compared to single-path RDMA. Our evaluation with an FPGA-based prototype demonstrates that compared with single-path RDMA, MP-RDMA can significantly improve the robustness under failures ( $2\times \sim 4\times $ higher throughput under 0.5%~10% link loss ratio) and improve the overall network utilization by up to 47%.

中文翻译：

---

MP-RDMA：在数据中心中通过多路径传输启用RDMA

RDMA的低延迟，高吞吐量和低CPU开销正变得越来越普遍。但是，在当前的数据中心中，RDMA仍然是单路径传输，容易发生故障，并且不足以利用丰富的并行网络路径。与以前的多路径方法（主要关注TCP）不同，本文提出了RDMA的多路径传输，即MP-RDMA，可有效利用数据中心中的丰富网络路径。MP-RDMA采用三种新颖的技术来应对有限的RDMA NIC片上存储器大小的挑战：1）a多路径ACK计时一种以拥塞感知的方式分配流量而不会产生每路径状态的机制；2）无序感知路径选择控制乱序传送的数据包级别的机制，从而使它们所需的元数据最小化；3）一个同步化确保在需要时按顺序更新内存的机制。通过所有这些技术，与单路径RDMA相比，MP-RDMA仅向每个连接状态添加66B。我们对基于FPGA的原型的评估表明，与单路径RDMA相比，MP-RDMA可以显着提高故障情况下的鲁棒性（ $ 2 \ times \ sim 4 \ times $ 在链路丢失率低于0.5％〜10％的情况下提高吞吐量），并将整体网络利用率提高多达47％。