It's not impossible; Linux already has a mechanism for this (alternatives, static keys), which allows patching code at runtime. It is used precisely for this ki

It's not impossible; Linux already has a mechanism for this (alternatives, static keys), which allows patching code at runtime. It is used precisely for this kind of thing, where you don't want the performance impact of branching every time to decide what code path to use. However, while it can practically eliminate code overhead, it can't eliminate data overhead. I'm guessing the RT stuff does add overhead to data structures, and alternatives wouldn't fix that.