Scheduling Analysis of UAV Flight Control Workloads using Raspberry Pi 5 Using PREEMPT_RT Linux
Luiz Giacomossi, Håkan Forsberg, Ivan Tomasic, Baran Çürüklü, Tommaso Cucinotta
TLDR
PREEMPT_RT Linux on Raspberry Pi 5 drastically reduces UAV flight control loop latencies, enabling real-time performance for integrated autonomy.
Key contributions
- Standard Linux kernel shows >9ms worst-case latency for UAV control on RPi 5 under stress.
- PREEMPT_RT Linux reduces worst-case latency by 88% to <225µs, enabling 250Hz control loops.
- Highlights direct kernel activation paths in PREEMPT_RT mitigate OS noise and scheduling variance.
- Identifies hardware memory contention as the primary source of residual jitter on modern SoCs.
Why it matters
This paper demonstrates the feasibility of using PREEMPT_RT Linux on low-cost hardware like Raspberry Pi 5 for critical UAV flight control. It provides crucial insights into real-time performance bottlenecks on modern SoCs, guiding future embedded system designs.
Original 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.
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