[PATCH v2] Move calc_load call out from xtime_lock protection

[Dimitri Sivanich]

The xtime_lock is being held for long periods on larger systems due
to an extensive amount of time being spent in calc_load(),
specifically here:
  do_timer->update_times->calc_load->count_active_tasks->nr_active()

On a 64 cpu system I've seen this take approximately 55 usec.
Presumably it would be worse on larger systems.  This causes other
cpus to be held off in places such as
scheduler_tick->sched_clock_tick waiting for the xtime_lock to be
released.