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From: John Stultz <john.stultz@linaro.org>
Date: Wed, 13 Jul 2016 13:13:11 -0700
Message-ID: <CALAqxLU76kVm8b5GNnSk25-Xk6D1efiWtwNJbY1th_pcN9Ks=g@mail.gmail.com>
Subject: Re: Severe performance regression w/ 4.4+ on Android due to cgroup
 locking changes
To: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        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>, Oleg Nesterov <oleg@redhat.com>
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On Wed, Jul 13, 2016 at 11:33 AM, Tejun Heo <tj@kernel.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