OSS + ELC EU 2026

Real-time Linux systems are often judged with timer-based benchmarks such as cyclictest, a useful baseline for wakeup latency caused by scheduling and system activity. Yet many embedded workloads are driven by external events, not periodic timers: GPIO edges, network packets, serial I/O, or other hardware interrupts. In these systems, the critical value is the latency from an interrupt to a high-priority task.

This talk asks how much end-to-end interrupt-driven latency timer-based benchmarks can explain, and where path-specific measurements are required.

We revisit RT evaluation on modern PREEMPT_RT Linux by combining cyclictest with measurements for GPIO interrupt paths, network receive paths, and interrupt-to-userspace wakeups. Across scenarios with CPU isolation, IRQ affinity tuning, and other common RT optimizations, we compare what each method reveals and misses. For selected setups, we also compare kernel/PREEMPT_RT revisions and use ftrace to locate latency sources.

Rather than treating one benchmark as a complete RT verdict, this session clarifies how timer-based results can inform, but not replace, measurements for practical interrupt-driven embedded workloads.