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

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Message-ID: <CALAqxLUDcwTzi=VmOtoCVX12bq51mRS0_M=3NkQxcCkhNPyVeg@mail.gmail.com>
Date:	Thu, 14 Jul 2016 09:54:00 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.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>,
	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 4:02 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Jul 13, 2016 at 03:39:37PM -0700, John Stultz wrote:
>>
>> But otherwise both patches look great and are working well!
>>
>> Do you mind marking them both for stable 4.4+?
>
> OK, looks like it does qualify in the "fix a notable performance or
> interactivity issue" category.
>
>> Tested-by: John Stultz <john.stultz@...aro.org>
>> Acked-by: John Stultz <john.stultz@...aro.org>
>>
>> Also, do make sure Dmitry gets the reported-by credit for the first patch.
>
> Done!  The updated first patch is below, and the second will follow.

So just as a heads up, while this patch *greatly* improved the
situation, apparently the occasional 7ms spikes (again, much better
then 80ms!) still seen are causing trouble when compared w/ the 4.1 or
earlier kernels (which I think kept things sub-ms - Dmitry, please
correct me).

So I wanted to dampen my enthusiasm a touch for this, as there may yet
further improvements needed.  I'll try to get some more info on this
as soon as I have details.

thanks
-john