- Use sched_throw() rather than replicating the same cpu_throw() code for
each architecture. This also allows the scheduler to use any locking it
may want to.
- Use the thread_lock() rather than sched_lock when preempting.
- The scheduler lock is not required to synchronize release_aps.
Tested by: kris, current@
Tested on: i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)