linux-kernel - Re: [RFC PATCH v2 19/25] sched/deadline: Allow deeper hierarchies of RT cgroups

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Message-ID: <aJ3y4YfcVQ-qVrxF@jlelli-thinkpadt14gen4.remote.csb>
Date: Thu, 14 Aug 2025 16:29:53 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Yuri Andriaccio <yurand2000@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org,
	Luca Abeni <luca.abeni@...tannapisa.it>,
	Yuri Andriaccio <yuri.andriaccio@...tannapisa.it>
Subject: Re: [RFC PATCH v2 19/25] sched/deadline: Allow deeper hierarchies of
 RT cgroups

Hi!

On 31/07/25 12:55, Yuri Andriaccio wrote:

...

> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 7b131630743..e263abcdc04 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -406,11 +406,42 @@ int dl_check_tg(unsigned long total)
>  	return 1;
>  }
>  
> -void dl_init_tg(struct sched_dl_entity *dl_se, u64 rt_runtime, u64 rt_period)
> +static inline bool is_active_sched_group(struct task_group *tg)
>  {
> +	struct task_group *child;
> +	bool is_active = 1;
> +
> +	// if there are no children, this is a leaf group, thus it is active
> +	list_for_each_entry_rcu(child, &tg->children, siblings) {
> +		if (child->dl_bandwidth.dl_runtime > 0) {
> +			is_active = 0;
> +		}
> +	}
> +	return is_active;
> +}
> +
> +static inline bool sched_group_has_active_siblings(struct task_group *tg)
> +{
> +	struct task_group *child;
> +	bool has_active_siblings = 0;
> +
> +	// if there are no children, this is a leaf group, thus it is active
> +	list_for_each_entry_rcu(child, &tg->parent->children, siblings) {
> +		if (child != tg && child->dl_bandwidth.dl_runtime > 0) {
> +			has_active_siblings = 1;
> +		}
> +	}
> +	return has_active_siblings;
> +}

...

> @@ -2216,7 +2228,14 @@ int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
>  	if (rt_group_sched_enabled() && tg->dl_bandwidth.dl_runtime == 0)
>  		return 0;
>  
> -	return 1;
> +	/* If one of the children has runtime > 0, cannot attach RT tasks! */
> +	list_for_each_entry_rcu(child, &tg->children, siblings) {
> +		if (child->dl_bandwidth.dl_runtime) {
> +			can_attach = 0;
> +		}
> +	}

Can we maybe reuse some of the methods above?

Thanks,
Juri