Re: [PATCH 23/24] sched/eevdf: Propagate min_slice up the cgroup hierarchy

[Tianchen Ding]

Hi Peter,

On 2024/7/27 18:27, Peter Zijlstra wrote:
> In the absence of an explicit cgroup slice configureation, make mixed
> slice length work with cgroups by propagating the min_slice up the
> hierarchy.

Will it be acceptable to introduce a cgroup interface (e.g., sth. like 
cpu.fair_runtime or cpu.fair_slice) to overwrite the caculated min_slice?
This could be useful in container scenarios.

> This ensures the cgroup entity gets timely service to service its
> entities that have this timing constraint set on them.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>   include/linux/sched.h |    1
>   kernel/sched/fair.c   |   57 +++++++++++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 57 insertions(+), 1 deletion(-)
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -542,6 +542,7 @@ struct sched_entity {
>   	struct rb_node			run_node;
>   	u64				deadline;
>   	u64				min_vruntime;
> +	u64				min_slice;
>   
>   	struct list_head		group_node;
>   	unsigned char			on_rq;
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -782,6 +782,21 @@ static void update_min_vruntime(struct c
>   	cfs_rq->min_vruntime = __update_min_vruntime(cfs_rq, vruntime);
>   }
>   
> +static inline u64 cfs_rq_min_slice(struct cfs_rq *cfs_rq)
> +{
> +	struct sched_entity *root = __pick_root_entity(cfs_rq);
> +	struct sched_entity *curr = cfs_rq->curr;
> +	u64 min_slice = ~0ULL;
> +
> +	if (curr && curr->on_rq)
> +		min_slice = curr->slice;
> +
> +	if (root)
> +		min_slice = min(min_slice, root->min_slice);

If a sched_delayed se keeps the min_slice, then the parent se will receive a 
shorter slice (from the sched_delayed se) than it should be. Is it a problem?

Thanks.