linux-kernel - Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting after every update

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Message-ID: <d38df868-bc65-4186-8ce4-12d8f37a16b5@redhat.com>
Date: Wed, 12 Mar 2025 09:55:20 -0400
From: Waiman Long <llong@...hat.com>
To: Juri Lelli <juri.lelli@...hat.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Waiman Long <llong@...hat.com>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Qais Yousef <qyousef@...alina.io>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Swapnil Sapkal <swapnil.sapkal@....com>,
 Shrikanth Hegde <sshegde@...ux.ibm.com>, Phil Auld <pauld@...hat.com>,
 luca.abeni@...tannapisa.it, tommaso.cucinotta@...tannapisa.it,
 Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH v3 4/8] sched/deadline: Rebuild root domain accounting
 after every update

On 3/12/25 6:09 AM, Juri Lelli wrote:
> On 12/03/25 10:53, Dietmar Eggemann wrote:
>> On 11/03/2025 15:51, Waiman Long wrote:
> ...
>
>>> You are right. cpuhp_tasks_frozen will be set in the suspend/resume
>>> case. In that case, we do need to add a cpuset helper to acquire the
>>> cpuset_mutex. A test patch as follows (no testing done yet):
> ...
>
>> This seems to work.
> Thanks for testing!
>
> Waiman, how do you like to proceed. Separate patch (in this case can you
> please send me that with changelog etc.) or incorporate your changes
> into my original patch and possibly, if you like, add Co-authored-by?
I think it will be better to merge into a single patch to avoid having a 
broken patch. It is up to you if you want me as a co-author. I don't 
really mind.
>
>> But what about a !CONFIG_CPUSETS build. In this case we won't have
>> this DL accounting update during suspend/resume since
>> dl_rebuild_rd_accounting() is empty.
> I unfortunately very much suspect !CPUSETS accounting is broken. But if
> that is indeed the case, it has been broken for a while. :(
Without CONFIG_CPUSETS, there will be one and only one global sched 
domain. Will this still be a problem?
>
> Will need to double check that, but I would probably do it later on
> separated from this set that at least seems to cure the most common
> cases. What do people think?

I am not aware of any distros without setting CONFIG_CPUSETS. So it is 
mostly a theoretical problem if there is one. So I would recommend going 
ahead with the current patch series instead of spending more time 
investigating this issue.

Cheers,
Longman