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

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Message-ID: <20160714173426.GC13434@redhat.com>
Date:	Thu, 14 Jul 2016 19:34:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	John Stultz <john.stultz@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Dmitry Shmidt <dimitrysh@...gle.com>,
	Rom Lemarchand <romlem@...gle.com>,
	Colin Cross <ccross@...gle.com>, Todd Kjos <tkjos@...gle.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
	locking changes

On 07/14, Peter Zijlstra wrote:
>
> But I really think that this Android usecase invalidates the premise of
> cgroups using a global lock.

Perhaps... but it would be nice to have a global lock for cgroups (and in
fact probably unify it with dup_mmap_sem). And we can't simply revert that
change now.

I am wondering if this use-case is really Android-specific or not. Because,
once again, we can add a boot option or even run-time knob for
cgroup_threadgroup_rwsem. If it is really Android-specific, we do not want
to penalize fork/exit by default.

Oleg.