I'm trying to understand the practical differences between the main Linux kernel scheduling policies – CFS, real‑time (FIFO/RR), and deadline. How does each one decide which task runs next, and what are the typical scenarios where one policy is clearly preferable over the others? Also, are there any pitfalls when switching a workload from the default scheduler to a real‑time one?
Linux kernel scheduling policies: How do they differ and when to use each?
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CFS is great for general‑purpose workloads because it balances fairness by giving each runnable task a virtual runtime slice, while FIFO/RR are best when you need deterministic latency (e.g., audio processing) – FIFO runs the highest‑priority task until it blocks, and RR adds a time‑slice for same‑priority tasks. The deadline scheduler shines for hard‑real‑time jobs where you can specify execution time, period, and deadline, letting the kernel guarantee that a task meets its timing constraints. Just remember that moving a non‑real‑time app to FIFO/RR can starve lower‑priority processes and break system responsiveness, so test with proper priority limits and keep a fallback to CFS for anything that isn’t strictly time‑critical.