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

[chenjinghuang <chenjinghuang2@huawei.com>]

On 6/25/2026 7:03 PM, 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
> 
Sorry, I forgot that sched_rt_runtime_us is currently set to 1000000,
so it should be the following case:
# cat /proc/sys/kernel/sched_rt_runtime_us
1000000
# echo 940000 > /proc/sys/kernel/sched_rt_runtime_us
-bash: echo: write error: Invalid argument
> With CONFIG_RT_GROUP_SCHED enabled, reducing the global RT quota
> causes the unchanged root cgroup quota to exceed the new global limit.
> The root cgroup quota should be updated accordingly when the global
> quota changes.
> 
> Adjust the root cgroup's RT quota whenever the global RT quota is
> modified.
> 
> Signed-off-by: Chen Jinghuang <chenjinghuang2@huawei.com>
> Reviewed-by: Ridong Chen <ridong.chen@linux.dev>
> Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
> ---
> Change since v1: https://lore.kernel.org/all/20260320013419.2493925-1-chenjinghuang2@huawei.com/
> - Rebase the patch onto mainline.
> ---
>  kernel/sched/rt.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index e474c31d8fe6..b1b082e365af 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2858,9 +2858,12 @@ static int sched_rt_global_validate(void)
>  #ifdef CONFIG_RT_GROUP_SCHED
>  	if (!rt_group_sched_enabled())
>  		return 0;
> +	
> +	u64 period = global_rt_period();
> +	u64 runtime = global_rt_runtime();
>  
>  	scoped_guard(mutex, &rt_constraints_mutex)
> -		return __rt_schedulable(NULL, 0, 0);
> +		return __rt_schedulable(&root_task_group, period, runtime);
>  #endif
>  	return 0;
>  }

Gently ping！