This directory is used to set IRQ to CPU affinity, which allows the system to connect a particular IRQ to only one CPU. Alternatively, it can exclude a CPU from handling any IRQs.

Each IRQ has its own directory, allowing for the individual configuration of each IRQ. The /proc/irq/prof_cpu_mask file is a bitmask that contains the default values for the smp_affinity file in the IRQ directory. The values in smp_affinity specify which CPUs handle that particular IRQ.

For more information about the /proc/irq/ directory, refer to the following installed documentation:

/usr/share/doc/kernel-doc-kernel_version/Documentation/filesystems/proc.txt