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>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b4c38bc..6eb4892 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -135,8 +135,8 @@
extern int nr_processes(void);
extern unsigned long nr_running(void);
extern unsigned long nr_uninterruptible(void);
-extern unsigned long nr_active(void);
extern unsigned long nr_iowait(void);
+extern void calc_global_load(void);
extern unsigned long get_parent_ip(unsigned long addr);