Scheduling techniques for hybrid circuit/packet networks

Abstract

A range of new datacenter switch designs combine wireless or optical circuit technologies with electrical packet switching to deliver higher performance at lower cost than traditional packet-switched networks. These "hybrid" networks schedule large traffic demands via a high-rate circuits and remaining traffic with a lower-rate, traditional packet-switches. Achieving high utilization requires an efficient scheduling algorithm that can compute proper circuit configurations and balance traffic across the switches. Recent proposals, however, provide no such algorithm and rely on an omniscient oracle to compute optimal switch configurations. Finding the right balance of circuit and packet switch use is difficult: circuits must be reconfigured to serve different demands, incurring non-trivial switching delay, while the packet switch is bandwidth constrained. Adapting existing crossbar scheduling algorithms proves challenging with these constraints. In this paper, we formalize the hybrid switching problem, explore the design space of scheduling algorithms, and provide insight on using such algorithms in practice. We propose a heuristic-based algorithm, Solstice that provides a 2.9× increase in circuit utilization over traditional scheduling algorithms, while being within 14% of optimal, at scale.

Costly circuits, submodular schedules and approximate Carathéodory Theorems

“…While Carathéodory's Theorem guarantees the existence of such a representation, an efficient algorithm to compute it has remained elusive so far. Our algorithm, which we christen Eclipse, has a performance that is at least half that of optimal for every instance of the traffic demands, and experimentally shows a strict and consistent improvement over the state-ofthe-art [40]. A key technical contribution here is the identification of a submodularity structure [5] in the problem, which allows us to make connections between submodular function maximization and the circuit switch scheduling problem with reconfiguration delay.…”

“…In this section, we present our model for a hybrid circuit-packet switched network fabric, and formally define our scheduling problem. Our model closely follows [40].…”

“…Previous measurement studies have shown that the inter-rack traffic in production data centers is sparse [40,8,3,51]. Over short periods of time (e.g., 10s of milliseconds), most nodes communicate with only a small number of other nodes (e.g., few to low tens).…”

“…Remark 1. Prior work [40,37] has considered the objective of covering the entire traffic demand in the least amount of time. For example, the ADJUST algorithm in [37] takes the traffic demand T as input and computes a schedule…”

“…Recent papers have proposed heuristic algorithms to address this scheduling problem. In Solstice [40], the authors present a greedy perfect-matching based heuristic for a hybrid electrical-optical switch. Experimental evaluations show Solstice performing well over a simple baseline (where the schedules are provided by a truncated Birkhoff-von Neumann decomposition of the traffic matrix), although no theoretical guarantees are presented.…”