用树莓派5测试实时内核，发现可将飞行控制延迟压至225微秒以下。
Scheduling Analysis of UAV Flight Control Workloads on PREEMPT_RT Linux Using a Raspberry Pi 5
- 对比软中断与实时唤醒路径，优化内核调度机制
- 标准内核最坏延迟超9毫秒，实时内核降至225微秒
- 飞行控制适合高实时性需求的嵌入式系统开发者
现代无人机架构越来越倾向于在通用操作系统上统一高层自主与底层飞行控制。然而，复杂的多核片上系统因共享资源竞争带来显著的时间不确定性。本文对树莓派5上的PREEMPT_RT Linux内核进行架构分析，重点考察内核激活路径（延迟执行的SoftIRQs与实时直接唤醒）对250 Hz控制回路的影响。结果表明，在高负载下，标准内核不适用，最坏延迟超过9毫秒；而PREEMPT_RT将最坏延迟降低近88%，降至225微秒以下，通过强制直接唤醒路径有效抑制了操作系统噪声。研究证明，虽然PREEMPT_RT解决了调度波动问题，但现代SoC上的残余抖动主要由硬件内存竞争驱动。
原文摘要 · Abstract (English)
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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