Real-time Linux (PREEMPT_RT)

In short: A real-time kernel guarantees that tasks react within a fixed time. This matters for machines, audio and robots. Linux can become a real-time system with the PREEMPT_RT patch set.

In more detail: After years of work, real-time capability became part of the main branch (since version 6.12 it is in the official kernel).

In detail

• Hard and soft: hard: the deadline is always met. Soft: the deadline is usually met.
• How it works: the kernel can be interrupted almost anywhere, locks become sleeping, interrupts run as threads.
• Use: industrial controllers, audio production (JACK/PipeWire), robotics (ROS), telecommunications.
• Scheduling classes: SCHED_FIFO, SCHED_RR, SCHED_DEADLINE.
• Measuring: cyclictest shows latencies.
• Alternatives: Xenomai, special RTOS such as FreeRTOS, Zephyr.

See also: Alternative kernels: Zen, XanMod, Liquorix and hardened, The Linux kernel at a glance