Re: Severe performance regression w/ 4.4+ on Android due to cgroup locking changes

[Oleg Nesterov]

On 07/14, John Stultz wrote:
>
> So I am seeing synchronize_sched called, and its taking the
> !rcu_gp_is_expedited path when I see the particularly bad latencies.
>
> I wonder if I just mucked up applying the patch?

Probably yes...

Just in case, could you try the patch below? Of course, without other
optimizations from Peter, this change makes cgroup_threadgroup_rwsem
much worse than a plain rw_semaphore.

Oleg.

--- x/kernel/cgroup.c
+++ x/kernel/cgroup.c
@@ -5605,6 +5605,8 @@ int __init cgroup_init(void)
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_dfl_base_files));
 	BUG_ON(cgroup_init_cftypes(NULL, cgroup_legacy_base_files));
 
+	rcu_sync_enter(&cgroup_threadgroup_rwsem.rss);
+
 	get_user_ns(init_cgroup_ns.user_ns);
 
 	mutex_lock(&cgroup_mutex);