High-Performance RoCE-Capable Multicast for Commodity RDMA Datacenters

Modern datacenter applications widely exhibit multicast communication patterns. Meanwhile, RDMA is emerging as the de-facto networking architecture to meet the stringent performance requirement of applications. However, existing multicast approaches fail to efficiently collaborate multicast with commodity RDMA transport, either causing inefficient multicast traffic transmission or being trapped in the insufficient end-host transport protocol. In this paper, we propose Cepheus, which delivers performance gains from both multicast (i.e., traffic reduction and transmission hop minimization) and RDMA transport (i.e., ultra-low latency, high throughput and low CPU overhead). Cepheus reuses RoCE as its transport layer and provides a RoCE-capable multicast primitive via in-network assistance. At its core, Cepheus builds on and goes beyond the native multicast architecture by exploiting more switch functionalities to tackle the incompatibilities between multicast flow structure and RoCE processing logic. We prototype Cepheus on an FPGA board, as a building block attached to an Ethernet switch. Extensive experiments demonstrate Cepheus inter-operates with commodity RoCE protocol and outperforms existing RDMA multicast schemes, e.g., $5.2\times $ faster multicast communication and $2.7\times $ higher replication throughput for distributed storage.