Everything Matters in Programmable Packet Scheduling (PACKS)#
NSDI '25 digest Program Core pick 28–30 April 2025
- Authors / tier: Albert Gran Alcoz (ETH Zürich); Balázs Vass (BME-TMIT); Pooria Namyar (USC); Behnaz Arzani (Microsoft Research); Gábor Rétvári (BME-TMIT); Laurent Vanbever (ETH Zürich). Core.
- Why: PIFO is the ideal programmable scheduler but can't be built at line rate in hardware. Prior approximations (SP-PIFO, AIFO) each capture only one of PIFO's two behaviors. This advances the "one scheduling abstraction on commodity switches" agenda that matters for anyone tuning FCT on Tofino-class hardware.
- What: PACKS approximates PIFO while capturing both required behaviors — scheduling order and admission control — which prior schemes handled only separately.
- How: Packets are tagged with ranks; PACKS uses a sliding window of recent ranks plus queue-occupancy to make admission decisions, and maps ranks across a small set of priority queues to minimize rank inversions. Reported: up to 7x and 15x fewer rank inversions than SP-PIFO and AIFO, up to 60% fewer drops vs SP-PIFO, and up to 33%/2.6x lower mean FCT for small flows under pFabric ranks.
- Where applicable: Existing programmable switches; implemented in P4 and shown to run at line rate on Intel Tofino. General technique within the constraints of fixed-queue hardware.