linux-kernel - Re: [PATCH 05/12] sched: Move sched_class::prio

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Message-ID: <21da68c5-e6ec-4ffd-81eb-e1fda13dd7af@arm.com>
Date: Thu, 15 Jan 2026 14:13:39 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>,
 K Prateek Nayak <kprateek.nayak@....com>, tj@...nel.org,
 linux-kernel@...r.kernel.org, mingo@...nel.org, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, longman@...hat.com,
 hannes@...xchg.org, mkoutny@...e.com, void@...ifault.com, arighi@...dia.com,
 changwoo@...lia.com, cgroups@...r.kernel.org, sched-ext@...ts.linux.dev,
 liuwenfang@...or.com, tglx@...utronix.de,
 Christian Loehle <christian.loehle@....com>, luca.abeni@...tannapisa.it
Subject: Re: [PATCH 05/12] sched: Move sched_class::prio_changed() into the
 change pattern

Hello Peter,

On 1/15/26 10:05, Peter Zijlstra wrote:
> On Thu, Jan 15, 2026 at 09:24:31AM +0100, Peter Zijlstra wrote:
>> On Wed, Jan 14, 2026 at 03:20:48PM +0100, Juri Lelli wrote:
>>
>>>> --- a/kernel/sched/syscalls.c
>>>> +++ b/kernel/sched/syscalls.c
>>>> @@ -639,7 +639,7 @@ int __sched_setscheduler(struct task_str
>>>>   		 * itself.
>>>>   		 */
>>>>   		newprio = rt_effective_prio(p, newprio);
>>>> -		if (newprio == oldprio)
>>>> +		if (newprio == oldprio && !dl_prio(newprio))
>>>>   			queue_flags &= ~DEQUEUE_MOVE;
>>>>   	}
>>> We have been using (improperly?) ENQUEUE_SAVE also to know when a new
>>> entity gets setscheduled to DEADLINE (or its parameters are changed) and
>>> it looks like this keeps that happening with DEQUEUE_MOVE. So, from a
>>> quick first look, it does sound good to me.
>> If this is strictly about tasks coming into SCHED_DEADLINE there are a
>> number of alternative options:
>>
>>   - there are the sched_class::switch{ing,ed}_to() callbacks;
>>   - there is (the fairly recent) ENQUEUE_CLASS.
>>
>> Anyway, let me break up this one patch into individual bits and write
>> changelogs. I'll stick them in queue/sched/urgent for now; hopefully
>> Pierre can given them a spin and report back if it all sorts his
>> problem).
> Now live at:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=sched/urgent
>
> Please test.
I don't see the balance_callback or the double clock update warnings 
anymore.

Thanks for the branch,
Regards,
Pierre