Eiffel: Efficient and Flexible Software Packet Scheduling

Packet scheduling determines the ordering of packets in a queuing data structure with respect to some ranking function that is mandated by a scheduling policy. It is the core component in many recent innovations in optimizing network performance and utilization. Packet scheduling is used for network resource allocation, meeting network-wide delay objectives, or providing isolation and differentiation of service. Our focus in this paper is on the design and deployment of packet scheduling in software. Software schedulers have several advantages including shorter development cycle and flexibility in functionality and deployment location. We substantially improve software packet scheduling performance, while maintaining its flexibility, by exploiting underlying features of packet ranking; the fact that packet ranks are integers that have predetermined ranges and that many packets will typically have equal rank. This allows us to rely on integer priority queues, compared to existing ranking algorithms, that rely on comparison-based priority queues that assume continuous ranks with infinite range. We introduce Eiffel, a novel programmable packet scheduling system. At the core of Eiffel is an integer priority queue based on the Find First Set (FFS) instruction and designed to support a wide range of policies and ranking functions efficiently. As an even more efficient alternative, we also propose a new approximate priority queue that can outperform FFS-based queues for some scenarios. To support flexibility, Eiffel introduces novel programming abstractions to express scheduling policies that cannot be captured by current, state of the art scheduler programming models. We evaluate Eiffel in a variety of settings and in both Kernel and userspace deployments. We show that it outperforms state of the art systems by 3-40x in terms of either number of cores utilized for network processing or number of flows given fixed processing capacity.