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

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Message-ID: <80a7cf2e-8c21-4c7d-9165-08608c569eab@arm.com>
Date: Tue, 13 Jan 2026 14:07:26 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Peter Zijlstra <peterz@...radead.org>,
 K Prateek Nayak <kprateek.nayak@....com>
Cc: tj@...nel.org, 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


On 1/13/26 12:56, Peter Zijlstra wrote:
> On Tue, Jan 13, 2026 at 12:53:09PM +0100, Peter Zijlstra wrote:
>> On Tue, Jan 13, 2026 at 04:35:02PM +0530, K Prateek Nayak wrote:
>>
>>> Does enabling WARN_DOUBLE_CLOCK warn of a double clock update before
>>> hitting this warning?
>> setup_new_dl_entity() -> update_rq_clock() seems like it will trip that
>> in this case.
> Something like so to fix: 9f239df55546 ("sched/deadline: Initialize dl_servers after SMP")
>
>
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -752,8 +752,6 @@ static inline void setup_new_dl_entity(s
>   	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>   	struct rq *rq = rq_of_dl_rq(dl_rq);
>   
> -	update_rq_clock(rq);
> -
>   	WARN_ON(is_dl_boosted(dl_se));
>   	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
>   
> @@ -1834,6 +1832,7 @@ void sched_init_dl_servers(void)
>   		rq = cpu_rq(cpu);
>   
>   		guard(rq_lock_irq)(rq);
> +		update_rq_clock(rq);
>   
>   		dl_se = &rq->fair_server;
>   
Yes right, enabling WARN_DOUBLE_CLOCK detects the double clock update 
and this fixes it.