linux-kernel - Re: [PATCH] sched/core: Remove double update_rq_clock() in __set_cpus_allowed_ptr

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Message-ID: <ee2746bd-1baa-48b1-bdaf-89c14a21b4fc@amd.com>
Date: Thu, 30 Oct 2025 09:34:00 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Hao Jia <jiahao.kernel@...il.com>, <mingo@...hat.com>,
	<peterz@...radead.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>
CC: <linux-kernel@...r.kernel.org>, Hao Jia <jiahao1@...iang.com>
Subject: Re: [PATCH] sched/core: Remove double update_rq_clock() in
 __set_cpus_allowed_ptr_locked()

Hello Hao,

On 10/29/2025 3:06 PM, Hao Jia wrote:
> From: Hao Jia <jiahao1@...iang.com>
> 
> Since commit d4c64207b88a ("sched: Cleanup the sched_change NOCLOCK usage"),
> update_rq_clock() is called in do_set_cpus_allowed() -> sched_change_begin()
> to update the rq clock. This results in a duplicate call update_rq_clock()
> in __set_cpus_allowed_ptr_locked().
> 
> While holding the rq lock and before calling do_set_cpus_allowed(),
> there is nothing that depends on an updated rq_clock.

I couldn't spot any dependency on rq_clock() until do_set_cpus_allowed()
either so please feel free to include:

Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>

-- 
Thanks and Regards,
Prateek

> 
> Therefore, remove the redundant update_rq_clock() in
> __set_cpus_allowed_ptr_locked() to avoid the warning about double
> rq clock updates.
> 
> Fixes: d4c64207b88a ("sched: Cleanup the sched_change NOCLOCK usage")
> Signed-off-by: Hao Jia <jiahao1@...iang.com>
> ---
>  kernel/sched/core.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1842285eac1e..1123cd0ddffb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2999,8 +2999,6 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
>  	unsigned int dest_cpu;
>  	int ret = 0;
>  
> -	update_rq_clock(rq);
> -
>  	if (kthread || is_migration_disabled(p)) {
>  		/*
>  		 * Kernel threads are allowed on online && !active CPUs,