Interrupt shielding

Using threaded interrupt handlers helps mitigate interrupt overhead by running some threads at a higher priority than interrupt handlers that do not impact real-time tasks. If you are using a multi-core processor, you can take a different approach and shield one or more cores from processing interrupts completely, allowing them to be dedicated to real-time tasks instead. This works either with a normal Linux kernel or a PREEMPT_RT kernel.

Achieving this is a question of pinning the real-time threads to one CPU and the interrupt handlers to a different one. You can set the CPU affinity of a thread or process using the taskset command-line tool, or you can use the sched_setaffinity(2) and pthread_setaffinity_np(3) functions.

To set the affinity of an interrupt, first note that there is a subdirectory for each interrupt number in /proc/irq/<IRQ number>. The control files for the interrupt are in there, including a CPU mask in smp_affinity. Write a bitmask...