Re: [PATCH 6/8] sched/eevdf: Add per cpu cached min_slice

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Sep 21, 2026 at 05:22:36PM +0200, Vincent Guittot wrote:
> In order to use min_slice during cpu selection, update a cached value when
> needed after en/dequeing a new task. This cached value includes current
> task.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>  kernel/sched/fair.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 739a3af60520..a01a88dde811 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1089,6 +1089,21 @@ static inline bool min_vruntime_update(struct sched_entity *se, bool exit)
>  RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,
>  		     run_node, min_vruntime, min_vruntime_update);
>  
> +static DEFINE_PER_CPU(u64, rq_min_slice) = INT_MAX;

Would it not be better to place this in struct rq, near data that is
already accessed in select_idle_siblings()? This more or less guarantees
a cache miss.

> +static u64 get_rq_min_slice(struct rq *rq)
> +{
> +	return READ_ONCE(per_cpu(rq_min_slice, cpu_of(rq)));
> +}
> +
> +static void __update_rq_min_slice(struct rq *rq)
> +{
> +	u64 min = cfs_rq_min_slice(&rq->cfs);
> +
> +	if (min != get_rq_min_slice(rq))
> +		WRITE_ONCE(per_cpu(rq_min_slice, cpu_of(rq)), min);
> +}
> +
>  /*
>   * Enqueue an entity into the rb-tree:
>   */