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

Tianchen Ding
2024-09-29T02:03:09Z

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@infradead.org>
> ---
> 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.