Scheduling Analysis of UAV Flight Control Workloads using Raspberry Pi 5 Using PREEMPT_RT Linux

TL;DR

This study evaluates the impact of PREEMPT RT Linux on UAV flight control workloads on Raspberry Pi 5, showing significant latency improvements but highlighting hardware contention as a residual jitter source.

Contribution

It provides an architectural analysis of PREEMPT RT Linux on Raspberry Pi 5, quantifying latency reductions and identifying hardware contention as a key jitter factor.

Findings

PREEMPT RT reduces worst-case latency by 88% under stress.

Standard kernel exhibits latencies over 9 ms, unsuitable for real-time UAV control.

Hardware memory contention remains a primary source of residual jitter.

Abstract

Modern UAV architectures increasingly aim to unify high-level autonomy and low-level flight control on a single General-Purpose Operating System (GPOS). However, complex multi-core System-on-Chips (SoCs) introduce significant timing indeterminism due to shared resource contention. This paper performs an architectural analysis of the PREEMPT RT Linux kernel on a Raspberry Pi 5, specifically isolating the impact of kernel activation paths (deferred execution SoftIRQs versus real-time direct activation) on a 250 Hz control loop. Results show that under heavy stress, the standard kernel is unsuitable, exhibiting worst-case latencies exceeding 9 ms. In contrast, PREEMPT RT reduced the worst-case latency by nearly 88 percent to under 225 microseconds, enforcing a direct wake-up path that mitigates OS noise. These findings demonstrate that while PREEMPT RT resolves scheduling variance, the residual jitter on modern SoCs is primarily driven by hardware memory contention.