What changes, if any, would an operating system need to implement to take full advantage of multicore systems? I ask this because I'm doing some research on parallel algorithms and the scheduler, for example, gets in my way of more theoretically-driven work. Are there other issues?
Besides what it has to do for taking full advantage of SMP, it's also convenient to be able to have some knowledge of hierarchy and relative costs, see this LWN article about scheduling domains.