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 | |
| 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>
| -rw-r--r-- | kernel/sched/fair.c | 11 | ||||
| -rw-r--r-- | kernel/sched/sched.h | 6 |
2 files changed, 14 insertions, 3 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d0cc03b3e70..c219bf8d704 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3387,6 +3387,14 @@ static int tg_load_down(struct task_group *tg, void *data) static void update_h_load(long cpu) { + struct rq *rq = cpu_rq(cpu); + unsigned long now = jiffies; + + if (rq->h_load_throttle == now) + return; + + rq->h_load_throttle = now; + rcu_read_lock(); walk_tg_tree(tg_load_down, tg_nop, (void *)cpu); rcu_read_unlock(); @@ -4293,11 +4301,10 @@ redo: env.src_rq = busiest; env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running); + update_h_load(env.src_cpu); more_balance: local_irq_save(flags); double_rq_lock(this_rq, busiest); - if (!env.loop) - update_h_load(env.src_cpu); /* * cur_ld_moved - load moved in current iteration 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 |