Modeling Buffer Occupancy in bittide Systems

TL;DR

This paper analyzes how elastic buffer occupancy behaves in bittide systems, providing formulas to optimize buffer sizes and reduce latency in distributed, clockless networks.

Contribution

It introduces a fluid model analysis of buffer occupancy in bittide systems and derives an explicit steady-state formula considering system parameters.

Findings

Buffer occupancy converges to a steady state.

Explicit formula for steady-state buffer occupancy.

Insights for optimizing buffer sizes and latency.

Abstract

The bittide mechanism enables logically synchronous computation across distributed systems by leveraging the continuous frame transmission inherent to wired networks such as Ethernet. Instead of relying on a global clock, bittide uses a decentralized control system to adjust local clock frequencies, ensuring all nodes operate with a consistent notion of time by utilizing elastic buffers at each node to absorb frequency variations. This paper presents an analysis of the steady-state occupancy of these elastic buffers, a critical factor influencing system latency. Using a fluid model of the bittide system, we prove that buffer occupancy converges and derive an explicit formula for the steady-state value in terms of system parameters, including network topology, physical latencies, and controller gains. This analysis provides valuable insights for optimizing buffer sizes and minimizing latency in bittide-based distributed systems.