Right now the SP build works because I am allowing (unthreaded) interrupts to steal the idleproc's context, and that only works because they can get the giant mutex without blocking (remember, the BSDI giant mutex is a blocking mutex, not a spin mutex). In the MP build the interrupts need to be able to block getting the giant mutex which means we need to implement heavy-weight interrupt threads at the very least before we can get anything working, because we are not allowed to block in the idleproc.