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Publications of SPCL

T. Bonato, A. Kubicek, A. Kabbani, A. Ghalayini, M. Besta, T. Hoefler:

 Spritz: Path-Aware Load Balancing in Low-Diameter Networks

(In Proceedings of the 40th IEEE International Parallel and Distributed Processing Symposium, presented in New Orleans, LA, USA, May 2026)

Abstract

Low-diameter topologies such as Dragonfly and Slim Fly are increasingly adopted in HPC and datacenter networks, yet existing load balancing techniques either rely on proprietary in-network mechanisms or fail to utilize the full path diversity of these topologies. We introduce Spritz, a flexible sender-based load balancing framework that shifts adaptive topology-aware routing to the endpoints using only standard Ethernet features. We propose two algorithms, Spritz-Scout and Spritz-Spray, that respectively explore and adaptively cache efficient paths using ECN, packet trimming, and timeout feedback. Through simulation on Dragonfly and Slim Fly topologies with over 1000 endpoints, Spritz outperforms ECMP, UGAL-L, and prior sender-based approaches by up to 1.8x in flow completion time under AI training and datacenter workloads, while offering robust failover with performance improvements of up to 25.4x under link failures, all without additional hardware support. Spritz enables datacenter-scale, commodity Ethernet networks to efficiently leverage low-diameter topologies, offering unified routing and load balancing for the Ultra Ethernet era.

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BibTeX

@inproceedings{bonato2026spritz,
  author={Tommaso Bonato and Ales Kubicek and Abdul Kabbani and Ahmad Ghalayini and Maciej Besta and Torsten Hoefler},
  title={{Spritz: Path-Aware Load Balancing in Low-Diameter Networks}},
  year={2026},
  month={05},
  booktitle={Proceedings of the 40th IEEE International Parallel and Distributed Processing Symposium},
  location={New Orleans, LA, USA},
  doi={10.48550/arXiv.2602.19567},
}