linux-kernel - Re: [PATCH] sched: cleanup sched_update

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Message-ID: <a08250a8-54e1-938c-54f1-5c357b3dda89@os.amperecomputing.com>
Date: Tue, 20 Jan 2026 12:00:29 -0800 (PST)
From: Shubhang Kaushik <shubhang@...amperecomputing.com>
To: Zhan Xusheng <zhanxusheng1024@...il.com>, linux-kernel@...r.kernel.org
cc: mingo@...nel.org, peterz@...radead.org, 
    Zhan Xusheng <zhanxusheng@...omi.com>
Subject: Re: [PATCH] sched: cleanup sched_update_scaling() return type and
 usage

Hello Zhan,

On Tue, 20 Jan 2026, Zhan Xusheng wrote:

> The function sched_update_scaling() always returned 0 and callers never
> checked its return value. This patch removes the return value and changes
> the function to return void for clarity.
>
> The usage of the return value in kernel/sched/debug.c has also been
> updated to reflect this change. This cleanup improves code readability
> and eliminates unnecessary logic.
>
> Tested:
> - Kernel compiled successfully
> - sched_update_scaling() invoked without errors
> - No regressions in scheduler-related functionality
>
> Signed-off-by: Zhan Xusheng <zhanxusheng@...omi.com>
> ---
> kernel/sched/debug.c | 3 +--
> kernel/sched/fair.c  | 4 +---
> kernel/sched/sched.h | 2 +-
> 3 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 41caa22e0680..d74c02297b42 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -189,8 +189,7 @@ static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
> 		return -EINVAL;
>
> 	sysctl_sched_tunable_scaling = scaling;
> -	if (sched_update_scaling())
> -		return -EINVAL;
> +	sched_update_scaling();

Okay. Good to remove a vestigial return value and dead -EINVAL check, as 
the function performs 'no-fail' math.

>
> 	*ppos += cnt;
> 	return cnt;
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e71302282671..234437ddd4c0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1004,7 +1004,7 @@ struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
> /**************************************************************
>  * Scheduling class statistics methods:
>  */
> -int sched_update_scaling(void)
> +void sched_update_scaling(void)
> {
> 	unsigned int factor = get_update_sysctl_factor();
>
> @@ -1012,8 +1012,6 @@ int sched_update_scaling(void)
> 	(normalized_sysctl_##name = sysctl_##name / (factor))
> 	WRT_SYSCTL(sched_base_slice);
> #undef WRT_SYSCTL
> -
> -	return 0;
> }

By changing this to void, we are asserting that the update is 
'fire-and-forget'. If we later need to add sanity check preventing 
for eg. slice that is too small, the return type might  need to
revert to int.

>
> static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 93fce4bbff5e..c9ef6cd7b754 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2168,7 +2168,7 @@ extern int group_balance_cpu(struct sched_group *sg);
> extern void update_sched_domain_debugfs(void);
> extern void dirty_sched_domain_sysctl(int cpu);
>
> -extern int sched_update_scaling(void);
> +extern void sched_update_scaling(void);
>
> static inline const struct cpumask *task_user_cpus(struct task_struct *p)
> {
> -- 
> 2.43.0
>
>

Regards,
Shubhang Kaushik