Re: [RFC PATCH] sched, cgroup: cgroup1 can also take the non-RUNTIME_INF min

[Phil Auld]

Hi,

On Tue, Sep 10, 2024 at 03:48:32PM +0800 Liu Song wrote:
> For the handling logic of child_quota, there is no need to distinguish
> between cgroup1 and cgroup2, so unify the handling logic here.
> 
> Signed-off-by: Liu Song <liusong@xxxxxxxxxxxxxxxxx>
> ---
>  kernel/sched/core.c | 21 +++++----------------
>  1 file changed, 5 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e752146e59a4..8418c67faa69 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9501,23 +9501,12 @@ static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
>  		parent_quota = parent_b->hierarchical_quota;
>  
>  		/*
> -		 * Ensure max(child_quota) <= parent_quota.  On cgroup2,
> -		 * always take the non-RUNTIME_INF min.  On cgroup1, only
> -		 * inherit when no limit is set. In both cases this is used
> -		 * by the scheduler to determine if a given CFS task has a
> -		 * bandwidth constraint at some higher level.

This comment is here for a reason. Please don't remove it. 

> +		 * Ensure max(child_quota) <= parent_quota.
>  		 */
> -		if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
> -			if (quota == RUNTIME_INF)
> -				quota = parent_quota;
> -			else if (parent_quota != RUNTIME_INF)
> -				quota = min(quota, parent_quota);
> -		} else {
> -			if (quota == RUNTIME_INF)
> -				quota = parent_quota;
> -			else if (parent_quota != RUNTIME_INF && quota > parent_quota)
> -				return -EINVAL;
> -		}
> +		if (quota == RUNTIME_INF)
> +			quota = parent_quota;
> +		else if (parent_quota != RUNTIME_INF)
> +			quota = min(quota, parent_quota);
>  	}
>  	cfs_b->hierarchical_quota = quota;
>

I don't think there is a need to optimize this slow path
to allow setting invalid values which have to be handled in
fast paths.   And this will change expected behavior.

So NAK.

Cheers,
Phil

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