* Remove possibility to temporarily disable small task packing.
* When small task packing target gets overloaded continue packing
threads on another core, but avoid migrating the already packed
ones.
Scheduler still tends to needlessly migrate threads to another cores
when under heavier load, but it is now much better than before.
* pin idle threads to their specific CPUs
* allow scheduler to implement SMP_MSG_RESCHEDULE handler
* scheduler_set_thread_priority() reworked
* at reschedule: enqueue old thread after dequeueing the new one
* Thread::scheduler_lock protects thread state, priority, etc.
* sThreadCreationLock protects thread creation and removal and list of
threads in team.
* Team::signal_lock and Team::time_lock protect list of threads in team
as well.
* Scheduler uses its own internal locking.
* No need for the atomically changed variables to be declared as
volatile.
* Drop support for atomically getting and setting unaligned data.
* Introduce atomic_get_and_set[64]() which works the same as
atomic_set[64]() used to. atomic_set[64]() does not return the
previous value anymore.
The flag main purpose is to avoid race conditions between event handler
and cancel_timer(). However, cancel_timer() is safe even without
using gSchedulerLock.
If the event is scheduled to happen on other CPU than the CPU that
invokes cancel_timer() then cancel_timer() either disables the event
before its handler starts executing or waits until the event handler
is done.
If the event is scheduled on the same CPU that calls cancel_timer()
then, since cancel_timer() disables interrupts, the event is either
executed before cancel_timer() or when the timer interrupt handler
starts running the event is already disabled.
Reads and writes to uid_t and gid_t are atomic anyway. The only real
problem that may happen here is inconsistent state of triples
effective_{u, g}id, saved_set_{u, g}id, real_{u, g}id, but team locks
protect us against that.
The fact that thread is waiting doesn't mean that it is nice to the others.
If the thread, indeed, waits for a longer time its penalty will be cancelled
anyway, however if the thread waits for a very short time do not count that
as being nice since lower priority threads didn't have much chance to run.
