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

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Date:   Fri, 14 Oct 2016 12:04:02 -0400
From:   Joseph Salisbury <joseph.salisbury@...onical.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
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>, omer.akram@...onical.com
Subject: Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes

On 10/14/2016 11:18 AM, Vincent Guittot wrote:
> Le Friday 14 Oct 2016 à 14:10:07 (+0100), Dietmar Eggemann a écrit :
>> On 14/10/16 09:24, Vincent Guittot wrote:
>>> On 13 October 2016 at 23:34, Vincent Guittot <vincent.guittot@...aro.org> wrote:
>>>> On 13 October 2016 at 20:49, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>>>> On 13/10/16 17:48, Vincent Guittot wrote:
>>>>>> On 13 October 2016 at 17:52, Joseph Salisbury
>>>>>> <joseph.salisbury@...onical.com> wrote:
>>>>>>> On 10/13/2016 06:58 AM, Vincent Guittot wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> On 12 October 2016 at 18:21, Joseph Salisbury
>>>>>>>> <joseph.salisbury@...onical.com> wrote:
>>>>>>>>> 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:
>> [...]
>>
>>>>> When I create a tg_root/tg_x/tg_y_1 and a tg_root/tg_x/tg_y_2 group, the tg_x->load_avg
>>>>> becomes > 6*1024 before any tasks ran in it.
>>>> This is normal as se->avg.load_avg is initialized to
>>>> scale_load_down(se->load.weight) and this se->avg.load_avg will be
>>>> added to tg_x[cpu]->cfs_rq->avg.load_avg when attached to the cfs_rq
>> Yeah, you right, even when I've created 50 second level groups,
>> tg_x->load_avg is ~6800.
>>
>> Could it have something to do with the fact that .se->load.weight = 2
>> for all these task groups? on a 64bit system?
> I don't think so, the problem really comes from tg->load_avg = 381697
> but sum of cfs_rq[cpu]->tg_load_avg_contrib = 1013 which is << tg->load_avg
> and cfs_rq[cpu]->tg_load_avg_contrib == cfs_rq[cpu]->avg.load_avg so we can't 
> expect any negative delta to remove this large value
>
>> In case we call  __update_load_avg(..., se->on_rq *
>> scale_load_down(se->load.weight), ...) we pass a weight argument of 0
>> for these se's.
>>
>> Does not happen with:
>>
>> -       if (shares < MIN_SHARES)
>> -               shares = MIN_SHARES;
>> +       if (shares < scale_load(MIN_SHARES))
>> +               shares = scale_load(MIN_SHARES);
>>
>> in  calc_cfs_shares().
>>
>> [...]
>>
>>
Adding Omer to CC list, as he is able to reproduce this bug.