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

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Message-ID: <CALAqxLWoMVzUuSJM0uKXO25s4toXMceLFdKngzGNsAX7-+q0FA@mail.gmail.com>
Date:	Wed, 13 Jul 2016 14:46:37 -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 2:42 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Jul 13, 2016 at 02:18:41PM -0700, Paul E. McKenney wrote:
>> On Wed, Jul 13, 2016 at 05:05:26PM -0400, Tejun Heo wrote:
>> > On Wed, Jul 13, 2016 at 02:03:15PM -0700, Paul E. McKenney wrote:
>> > > Take the patch that I just sent out and make the choice of normal
>> > > vs. expedited depend on CONFIG_PREEMPT_RT or whatever the -rt guys are
>> > > calling it these days.  Is there a low-latency Kconfig option other
>> > > than CONFIG_NO_HZ_FULL?
>> >
>> > Sounds like a plan to me.
>>
>> I like the way we like each other's idea.  Mutually assured laziness?  ;-)
>
> But here is what mine might look like.  Untested, probably does
> not even build.  Note that the default is -no- expediting, use the
> rcusync.expedited kernel parameter to enable it.

I was working on something similar, but using a config option. Would
adding a config option for the default make sense here, since I'd
probably prefer to have one less thing to always specify on the
cmdline?

thanks
-john