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

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Date:   Fri, 14 Oct 2016 14:10:07 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Joseph Salisbury <joseph.salisbury@...onical.com>,
        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 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?

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().

[...]