Peter Zijlstra a35b6466aa sched, cgroup: Reduce rq->lock hold times for large cgroup hierarchies ... Peter Portante reported that for large cgroup hierarchies (and or on large CPU counts) we get immense lock contention on rq->lock and stuff stops working properly. His workload was a ton of processes, each in their own cgroup, everybody idling except for a sporadic wakeup once every so often. It was found that: schedule() idle_balance() load_balance() local_irq_save() double_rq_lock() update_h_load() walk_tg_tree(tg_load_down) tg_load_down() Results in an entire cgroup hierarchy walk under rq->lock for every new-idle balance and since new-idle balance isn't throttled this results in a lot of work while holding the rq->lock. This patch does two things, it removes the work from under rq->lock based on the good principle of race and pray which is widely employed in the load-balancer as a whole. And secondly it throttles the update_h_load() calculation to max once per jiffy. I considered excluding update_h_load() for new-idle balance all-together, but purely relying on regular balance passes to update this data might not work out under some rare circumstances where the new-idle busiest isn't the regular busiest for a while (unlikely, but a nightmare to debug if someone hits it and suffers). Cc: pjt@google.com Cc: Larry Woodman <lwoodman@redhat.com> Cc: Mike Galbraith <efault@gmx.de> Reported-by: Peter Portante <pportant@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/n/tip-aaarrzfpnaam7pqrekofu8a6@git.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>		2012-08-13 18:41:54 +02:00
..
auto_group.c
auto_group.h
clock.c
core.c	sched: Use task_rq_unlock() in __sched_setscheduler()	2012-07-26 11:46:59 +02:00
cpupri.c	sched: Fix minor code style issues	2012-07-26 11:47:00 +02:00
cpupri.h
debug.c
fair.c	sched, cgroup: Reduce rq->lock hold times for large cgroup hierarchies	2012-08-13 18:41:54 +02:00
features.h
idle_task.c	sched/nohz: Rewrite and fix load-avg computation -- again	2012-07-05 20:58:13 +02:00
Makefile
rt.c	sched/rt: Fix lockdep annotation within find_lock_lowest_rq()	2012-06-06 16:52:26 +02:00
sched.h	sched, cgroup: Reduce rq->lock hold times for large cgroup hierarchies	2012-08-13 18:41:54 +02:00
stats.c
stats.h
stop_task.c