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

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Date:	Wed, 13 Jul 2016 13:13:11 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
 locking changes

On Wed, Jul 13, 2016 at 11:33 AM, Tejun Heo <tj@...nel.org> wrote:
> On Wed, Jul 13, 2016 at 02:21:02PM -0400, Tejun Heo wrote:
>> One interesting thing to try would be replacing it with a regular
>> non-percpu rwsem and see how it behaves.  That should easily tell us
>> whether this is from actual contention or artifacts from percpu_rwsem
>> implementation.
>
> So, something like the following.  Can you please see whether this
> makes any difference?

Yea. So this brings it down for me closer to what we're seeing with
the Dmitry's patch reverting the two problematic commits, usually
10-50us with one early spike at 18ms.

thanks
-john