Extending R2P2 with Congestion Control and Request-Level Scheduling

Distributed low-latency datacenter applications must meet strict service-level objectives in the order of microseconds. R2P2 is a novel datacenter transport protocol designed for such services. This work extends R2P2 with congestion control and request-level scheduling. It provides a configurable upper bound to in-network queuing using the idleness of the ToR-to-host link as the congestion signal. It also reduces the mean and tail RPC latency by minimizing head-of-line blocking in the network through shortest remaining processing time scheduling. The receiver driven scheduling mechanism is general and can support a variety of scheduling policies. The extension improves the performance of R2P2 under network load by at least 23% and up to two orders of magnitude. Finally, it enables R2P2 to perform similarly to a theoretically near-optimal, clean-slate transport protocol design.