linux-kernel - Re: [RFC PATCH v4 11/28] sched/deadline: Account rt-cgroups bandwidth in deadline tasks schedulability tests.

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Message-ID: <aW45EAK-aJnrzajj@jlelli-thinkpadt14gen4.remote.csb>
Date: Mon, 19 Jan 2026 15:00:48 +0100
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 v4 11/28] sched/deadline: Account rt-cgroups
 bandwidth in deadline tasks schedulability tests.

Hello,

On 01/12/25 13:41, Yuri Andriaccio wrote:
> From: luca abeni <luca.abeni@...tannapisa.it>
> 
> Account the rt-cgroups hierarchy's reserved bandwidth in the
> schedulability test of deadline entities. This mechanism allows to
> completely reserve portion of the rt-bandwidth to rt-cgroups even if
> they do not use all of it.
> 
> Account for the rt-cgroups' reserved bandwidth also when changing the
> total dedicated bandwidth for real time tasks.
> 
> Co-developed-by: Alessio Balsini <a.balsini@...up.it>
> Signed-off-by: Alessio Balsini <a.balsini@...up.it>
> Co-developed-by: Andrea Parri <parri.andrea@...il.com>
> Signed-off-by: Andrea Parri <parri.andrea@...il.com>
> Co-developed-by: Yuri Andriaccio <yurand2000@...il.com>
> Signed-off-by: Yuri Andriaccio <yurand2000@...il.com>
> Signed-off-by: luca abeni <luca.abeni@...tannapisa.it>
> ---
>  kernel/sched/deadline.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 4f43883a65..089fd2c9b7 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -213,8 +213,15 @@ void __dl_add(struct dl_bw *dl_b, u64 tsk_bw, int cpus)
>  static inline bool
>  __dl_overflow(struct dl_bw *dl_b, unsigned long cap, u64 old_bw, u64 new_bw)
>  {
> +	u64 dl_groups_root = 0;
> +
> +#ifdef CONFIG_RT_GROUP_SCHED
> +	dl_groups_root = to_ratio(root_task_group.dl_bandwidth.dl_period,
> +				  root_task_group.dl_bandwidth.dl_runtime);
> +#endif
>  	return dl_b->bw != -1 &&
> -	       cap_scale(dl_b->bw, cap) < dl_b->total_bw - old_bw + new_bw;
> +	       cap_scale(dl_b->bw, cap) < dl_b->total_bw - old_bw + new_bw
> +					+ cap_scale(dl_groups_root, cap);
>  }
> 
>  static inline
> @@ -3147,10 +3154,16 @@ int sched_dl_global_validate(void)
>  	u64 period = global_rt_period();
>  	u64 new_bw = to_ratio(period, runtime);
>  	u64 cookie = ++dl_cookie;
> +	u64 dl_groups_root = 0;
>  	struct dl_bw *dl_b;
> -	int cpu, cpus, ret = 0;
> +	int cpu, cap, cpus, ret = 0;
>  	unsigned long flags;
> 
> +#ifdef CONFIG_RT_GROUP_SCHED
> +	dl_groups_root = to_ratio(root_task_group.dl_bandwidth.dl_period,
> +				  root_task_group.dl_bandwidth.dl_runtime);
> +#endif

Can we move these ifdefs in some header and use helper functions
instead?

Thanks,
Juri