Re: [RFC PATCH V2 1/3] sched/fair: Fixup-wake_up_sync-vs-DELAYED_DEQUEUE

[Vincent Guittot]

On Mon, 3 Mar 2025 at 11:56, Xuewen Yan <xuewen.yan@xxxxxxxxxx> wrote:
>
> Delayed dequeued feature keeps a sleeping task enqueued until its
> lag has elapsed. As a result, it stays also visible in rq->nr_running.
> So when in wake_affine_idle(), we should use the real running-tasks
> in rq to check whether we should place the wake-up task to
> current cpu.
> On the other hand, add a helper function to return the nr-delayed.
>
> Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
> Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
> V2:
> - add helper function (Vincent)
> ---
>  kernel/sched/fair.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1c0ef435a7aa..a354f29c4f6f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7181,6 +7181,11 @@ static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>         return true;
>  }
>
> +static inline unsigned int cfs_h_nr_delayed(struct rq *rq)
> +{
> +       return (rq->cfs.h_nr_queued - rq->cfs.h_nr_runnable);
> +}
> +
>  #ifdef CONFIG_SMP
>
>  /* Working cpumask for: sched_balance_rq(), sched_balance_newidle(). */
> @@ -7342,8 +7347,12 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
>         if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
>                 return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu;
>
> -       if (sync && cpu_rq(this_cpu)->nr_running == 1)
> -               return this_cpu;
> +       if (sync) {
> +               struct rq *rq = cpu_rq(this_cpu);
> +
> +               if ((rq->nr_running - cfs_h_nr_delayed(rq)) == 1)
> +                       return this_cpu;
> +       }
>
>         if (available_idle_cpu(prev_cpu))
>                 return prev_cpu;
> --
> 2.25.1
>