linux-kernel - Re: [PATCH 0/10 v2] sched/fair: Fix statistics with delayed dequeue

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Message-ID: <e97196fe-3ab2-4ad5-ba88-e7f635fbf957@arm.com>
Date: Mon, 2 Dec 2024 14:52:41 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>,
 Luis Machado <luis.machado@....com>
Cc: Mike Galbraith <efault@....de>, mingo@...hat.com, peterz@...radead.org,
 juri.lelli@...hat.com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
 kprateek.nayak@....com, pauld@...hat.com
Subject: Re: [PATCH 0/10 v2] sched/fair: Fix statistics with delayed dequeue

On 02/12/2024 10:59, Vincent Guittot wrote:
> On Mon, 2 Dec 2024 at 10:23, Luis Machado <luis.machado@....com> wrote:
>>
>> On 12/2/24 09:17, Vincent Guittot wrote:
>>> On Sun, 1 Dec 2024 at 14:30, Mike Galbraith <efault@....de> wrote:
>>>>
>>>> Greetings,
>>>>
>>>> On Fri, 2024-11-29 at 17:17 +0100, Vincent Guittot wrote:

[...]

>>>>> h_nr_runnable is used in several places to make decision on load balance:
>>>>>   - PELT runnable_avg
>>>>>   - deciding if a group is overloaded or has spare capacity
>>>>>   - numa stats
>>>>>   - reduced capacity management
>>>>>   - load balance between groups
>>>>
>>>> I took the series for a spin in tip v6.12-10334-gb1b238fba309, but
>>>> runnable seems to have an off-by-one issue, causing it to wander ever
>>>> further south.
>>>>
>>>> patches 1-3 applied.
>>>>   .h_nr_runnable                 : -3046
>>>>   .runnable_avg                  : 450189777126
>>>
>>> Yeah, I messed up something around finish_delayed_dequeue_entity().
>>> I'm' going to prepare a v3>
>>
>> Maybe something similar to what I ran into here?
>>
>> https://lore.kernel.org/lkml/6df12fde-1e0d-445f-8f8a-736d11f9ee41@arm.com/
> 
> I'm going to have a look

Looks like this is not an issue anymore since commit 98442f0ccd82
("sched: Fix delayed_dequeue vs switched_from_fair()") removed
finish_delayed_dequeue_entity() from switched_from_fair() in the meantime.

[...]