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

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Message-ID: <ef8d8e46-06eb-46c1-9402-d292c2eb51f9@amd.com>
Date: Tue, 13 Jan 2026 16:35:02 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Pierre Gondois <pierre.gondois@....com>, Peter Zijlstra
	<peterz@...radead.org>, <tj@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <mingo@...nel.org>,
	<juri.lelli@...hat.com>, <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>
Subject: Re: [PATCH 05/12] sched: Move sched_class::prio_changed() into the
 change pattern

Hello Pierre,

On 1/13/2026 4:15 PM, Pierre Gondois wrote:
> Hello Prateek,
> 
> On 1/13/26 05:12, K Prateek Nayak wrote:
>> Hello Pierre,
>>
>> On 1/13/2026 2:14 AM, Pierre Gondois wrote:
>>> Hello Peter,
>>>
>>> It seems this patch:
>>> 6455ad5346c9 ("sched: Move sched_class::prio_changed() into the change pattern")
>>> is triggering the following warning:
>>> rq_pin_lock()
>>> \-WARN_ON_ONCE(rq->balance_callback && rq->balance_callback != &balance_push_callback);
>> Can you check if the following solution helps your case too:
>> https://lore.kernel.org/all/20260106104113.GX3707891@noisy.programming.kicks-ass.net/
>>
> I can still see the issue.
> It seems the task deadline is also updated in:
> sched_change_end()
> \-enqueue_task_dl()
>   \-enqueue_dl_entity()
>     \-setup_new_dl_entity()
>       \-replenish_dl_new_period()
> if the task's period finished.

Ah! Got it. Thank you for testing the fix.

I'm curious, why is setup_new_dl_entity() doing an
update_rq_clock()? That can advance the rq->clock and make it look like
we need a replenish.

Does enabling WARN_DOUBLE_CLOCK warn of a double clock update before
hitting this warning?

> 
> So in sched_change_end(), the task priority (i.e. p->dl.deadline) is updated.
> This results in having an old_deadline earlier than the new p->dl.deadline.
> Thus the rq->balance_callback:
> 
> prio_changed_dl() {
> ...
> if (dl_time_before(old_deadline, p->dl.deadline))
>   deadline_queue_pull_task(rq);
> ...
> }
> 

Thank you for your analysis.

-- 
Thanks and Regards,
Prateek