In high-speed interconnection networks, credit-based flow control is widely deployed at the link layer to ensure data lossless. In this case, each credit schedules data on a one-hop fixed link. When employing credit in higher layers, e.g. transport layer, credit needs to be transmitted through multiple hops to realize end-to-end scheduling. In credit-based transports, each credit is transmitted to the data sender through a credit path, in return, each data packet is sent to the data receiver through a data path. In modern high-speed data centers that deploy topologies with multiple equivalent paths, the multi-hop credit can be routed into diverse paths. For the credit-based transports that require strong path-consistency between the data path and the credit path, properly routing credits becomes significant to improve data transmission efficiency. However, existing solutions lack consideration for exploiting multiple paths, this limits them to be single-path transports and affects their performance.

To optimize the end-to-end latency and fully utilize the network resources, this paper presents MP-CREDIT, the first multi-path credit protocol designed for strong path-consistency transports. MP-CREDIT leverages credit spray to uniformly balance the traffic on multiple paths, and employs sequence-free feedback control to remedy credit out-of-order. Besides, we develop path probing for MP-CREDIT to handle path failures. Compared to state-of-the-art credit-based transport, MP-CREDIT reduces average flow completion times to 0.53x in the realistic workloads, greatly improves the throughput to 1.28x with permutation traffic, and achieves much better fairness in asymmetry network.

在高速互连网络中，基于信用的流量控制广泛部署在链路层，以确保数据无损。在这种情况下，每个信用将数据安排在单跳固定链接上。当在较高层（例如，传输层）中使用信用时，需要通过多跳来传输信用以实现端到端调度。在基于信用的传输中，每个信用都通过信用路径传输到数据发送方，作为回报，每个数据包都通过数据路径发送给数据接收方。在部署具有多个等效路径的拓扑的现代高速数据中心中，可以将多跳信用路由到不同的路径中。对于需要在数据路径和信用路径之间具有强路径一致性的基于信用的传输，正确路由信用会变得很重要，以提高数据传输效率。

为了优化端到端延迟并充分利用网络资源，本文介绍了MP-CREDIT，这是第一种为强路径一致性传输而设计的多路径信用协议。MP-CREDIT利用信用喷雾来均匀地平衡多条路径上的流量，并采用无序列的反馈控制来纠正信用不正常的情况。此外，我们为MP-CREDIT开发路径探测以处理路径故障。与最先进的基于信用的传输相比，MP-CREDIT将实际工作负载中的平均流完成时间减少到0.53倍，在排列流量的情况下将吞吐量大大提高到1.28倍，并且在不对称网络中实现了更好的公平性。