Conservative birq behaviour. The birq on start tries to link IRQs to CPU using current affinity. It doesn't change affinity if IRQ doesn't have affinity to multiply CPUs. It doesn't change IRQ affinity if number of interrupts is 0.
In some cases the OS can't move IRQ to specified CPU. To keep the state consistent the birq analyzes real IRQ affinity on each iteration.
Add new option --load-limit. If the loading of CPU is greater than this limit then no IRQs can't be moved to this CPU. It stabilizes the behaviour on a high load.