- idle task becomes a pseudo task which is never scheduled. It is never put on
any run queue and never enters userspace. An entry for this task still remains
in the process table for time accounting
- Instead of panicing if there is not process to schedule, pick_proc() returns
NULL which is a signal to put the cpu in an idle state and set everything in
such a way that after receiving and interrupt it looks like idle task was
preempted
- idle task is set non-preemptible to avoid handling in the timer interrupt code
which make userspace scheduling simpler as idle task does not need to be
handled as a special case.