commit dce48a84adf1806676319f6f480e30a6daa012f9
author Thomas Gleixner <tglx@linutronix.de> Sat Apr 11 10:43:41 2009 +0200
committer Thomas Gleixner <tglx@linutronix.de> Fri May 15 15:32:45 2009 +0200
tree 79151f5d31d9c3dcdc723ab8877cb943b944890e
parent 2ff799d3cff1ecb274049378b28120ee5c1c5e5f

sched, timers: move calc_load() to scheduler

Dimitri Sivanich noticed that xtime_lock is held write locked across
calc_load() which iterates over all online CPUs. That can cause long
latencies for xtime_lock readers on large SMP systems. 

The load average calculation is an rough estimate anyway so there is
no real need to protect the readers vs. the update. It's not a problem
when the avenrun array is updated while a reader copies the values.

Instead of iterating over all online CPUs let the scheduler_tick code
update the number of active tasks shortly before the avenrun update
happens. The avenrun update itself is handled by the CPU which calls
do_timer().

[ Impact: reduce xtime_lock write locked section ]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>