linux-kernel - Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

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Message-ID: <57FE6302.6060103@canonical.com>
Date:   Wed, 12 Oct 2016 12:21:22 -0400
From:   Joseph Salisbury <joseph.salisbury@...onical.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Galbraith <efault@....de>
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

On 10/12/2016 08:20 AM, Vincent Guittot wrote:
> On 8 October 2016 at 13:49, Mike Galbraith <efault@....de> wrote:
>> On Sat, 2016-10-08 at 13:37 +0200, Vincent Guittot wrote:
>>> On 8 October 2016 at 10:39, Ingo Molnar <mingo@...nel.org> wrote:
>>>> * Peter Zijlstra <peterz@...radead.org> wrote:
>>>>
>>>>> On Fri, Oct 07, 2016 at 03:38:23PM -0400, Joseph Salisbury wrote:
>>>>>> Hello Peter,
>>>>>>
>>>>>> A kernel bug report was opened against Ubuntu [0].  After a
>>>>>> kernel
>>>>>> bisect, it was found that reverting the following commit
>>>>>> resolved this bug:
>>>>>>
>>>>>> commit 3d30544f02120b884bba2a9466c87dba980e3be5
>>>>>> Author: Peter Zijlstra <peterz@...radead.org>
>>>>>> Date:   Tue Jun 21 14:27:50 2016 +0200
>>>>>>
>>>>>>     sched/fair: Apply more PELT fixes
>>> This patch only speeds up the update of task group load in order to
>>> reflect the new load balance but It should not change the final value
>>> and as a result the final behavior. I will try to reproduce it in my
>>> target later today
>> FWIW, I tried and failed w/wo autogroup on 4.8 and master.
> Me too
>
> Is it possible to get some dump of  /proc/sched_debug while the problem occurs ?
>
> Vincent
>
>>         -Mike

The output from /proc/shed_debug can be seen here:
http://paste.ubuntu.com/23312351/

Ingo, the latest scheduler bits also still exhibit the bug:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git