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Date: Thu, 14 Jul 2016 19:13:12 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
        Ingo Molnar <mingo@redhat.com>, lkml <linux-kernel@vger.kernel.org>,
        Dmitry Shmidt <dimitrysh@google.com>,
        Rom Lemarchand <romlem@google.com>, Colin Cross <ccross@google.com>,
        Todd Kjos <tkjos@google.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
	locking changes
Message-ID: <20160714171311.GB13434@redhat.com>
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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);