Providing Near-Optimal Fair-Queueing Guarantees at Round-Robin Amortized Cost

Round-robin schedulers are the most efficient solution for providing strong QoS guarantees on high-speed links. Yet these schedulers suffer from a high worst-case delay with respect to an ideal, perfectly fair service. More costly schedulers are needed to provide better service guarantees. In this paper we tackle this problem by proposing a simple modification scheme for reducing the amortized execution time of fair-queueing schedulers. We prove that, applying this scheme to existing accurate schedulers, we can define new schedulers providing near-optimal service guarantees at an amortized computational cost close to that of just Deficit Round Robin (DRR). Finally, we show Quick Fair Queueing Plus (QFQ+), a new scheduler obtained by applying our scheme to QFQ. QFQ+ replaced QFQ in the Linux kernel. According to our experimental results, and exactly in the scenarios where QFQ+ provides better service guarantees than a round-robin scheduler, the time and the energy needed to process packets with QFQ+ is lower than with DRR.