Re: [RESEND] In cgroup v2, setting a smaller value for sched_rt_runtime_us fails.

[chenjinghuang <chenjinghuang2@huawei.com>]

On 3/20/2026 9:34 AM, Chen Jinghuang wrote:
> For example:
> 
> 	# cat /proc/sys/kernel/sched_rt_runtime_us
> 	950000
> 	# echo 940000 > /proc/sys/kernel/sched_rt_runtime_us
> 	-bash: echo: write error: Invalid argument
> 
> This occurs because when the global RT quota is reduced while the root
> cgroup’s ratio remains unchanged, the root cgroup’s proportion ends up
> exceeding the global RT ratio. This is unreasonable: the root cgroup’s
> ratio should be updated when the global RT ratio changes.
> 
> This patch ensures the root cgroup’s RT quota is adjusted whenever the
> global RT quota is modified.
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
> Reviewed-by: Chen Jinghuang <chenjinghuang2@huawei.com>
> ---
>  kernel/sched/rt.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index f1867fe8e5c5..30770ba7be4e 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2814,9 +2814,11 @@ long sched_group_rt_period(struct task_group *tg)
>  static int sched_rt_global_constraints(void)
>  {
>  	int ret = 0;
> +	u64 period = global_rt_period();
> +	u64 runtime = global_rt_runtime();
>  
>  	mutex_lock(&rt_constraints_mutex);
> -	ret = __rt_schedulable(NULL, 0, 0);
> +	ret = __rt_schedulable(&root_task_group, period, runtime);
>  	mutex_unlock(&rt_constraints_mutex);
>  
>  	return ret;
> @@ -2856,6 +2858,14 @@ static int sched_rt_global_validate(void)
>  
>  static void sched_rt_do_global(void)
>  {
> +#ifdef CONFIG_RT_GROUP_SCHED
> +	if (!rt_group_sched_enabled())
> +		return;
> +
> +	WARN_ON_ONCE(tg_set_rt_bandwidth(&root_task_group,
> +					global_rt_period(),
> +					global_rt_runtime()));
> +#endif
>  }
>  
>  static int sched_rt_handler(const struct ctl_table *table, int write, void *buffer,
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