Re: [RFC PATCH V3 4/6] sched/deadline: Introduce deadline servers

[Valentin Schneider]

On 08/06/23 17:58, Daniel Bristot de Oliveira wrote:
> @@ -2033,9 +2147,20 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
>  	struct task_struct *p;
>  
>  	p = pick_task_dl(rq);
> -	if (p)
> +	if (!p)
> +		return p;
> +
> +	/*
> +	 * XXX: re-check !dl_server, changed from v2 because of
> +	 * pick_next_task_dl change
> +	 */
> +	if (!dl_server(&p->dl))
>  		set_next_task_dl(rq, p, true);
>

Should this be

       if (!p->server)

instead? AFAICT dl_server(&p->dl) can never be true since there's no
pi_se-like link to the server via the dl_se, only via the task_struct, and
the server pick cannot return the server itself (as it's a pure sched_entity).

> +	/* XXX not quite right */
> +	if (hrtick_enabled(rq))
> +		start_hrtick_dl(rq, &p->dl);
> +

IIUC that got hauled out of set_next_task_dl() to cover the case where we
pick the server (+ the server pick) and want to more thoroughly enforce the
server's bandwidth. If so, what's the issue with starting the hrtick here?

>  	return p;
>  }
>