diff options
author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2012-08-08 21:46:40 +0200 |
---|---|---|
committer | Thomas Gleixner <tglx@linutronix.de> | 2012-08-13 18:41:54 +0200 |
commit | a35b6466aabb051568b844e8c63f87a356d3d129 (patch) | |
tree | a5d38cce8290a60f6729f97591cfa25d545c6474 /kernel/sched/sched.h | |
parent | b9403130a5350fca59a50ed11c198cb8c7e54119 (diff) |
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>
Diffstat (limited to 'kernel/sched/sched.h')
-rw-r--r-- | kernel/sched/sched.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index c35a1a7dd4d..531411b1044 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -374,7 +374,11 @@ struct rq { #ifdef CONFIG_FAIR_GROUP_SCHED /* list of leaf cfs_rq on this cpu: */ struct list_head leaf_cfs_rq_list; -#endif +#ifdef CONFIG_SMP + unsigned long h_load_throttle; +#endif /* CONFIG_SMP */ +#endif /* CONFIG_FAIR_GROUP_SCHED */ + #ifdef CONFIG_RT_GROUP_SCHED struct list_head leaf_rt_rq_list; #endif |