linux-kernel - Re: [PATCH v3 2/5] sched/deadline: Add dl_bw

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Date:   Fri, 22 May 2020 16:58:02 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Wei Wang <wvw@...gle.com>, Quentin Perret <qperret@...gle.com>,
        Alessio Balsini <balsini@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        Qais Yousef <qais.yousef@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] sched/deadline: Add dl_bw_capacity()

On 20/05/20 15:42, Dietmar Eggemann wrote:
> Capacity-aware SCHED_DEADLINE Admission Control (AC) needs root domain
> (rd) CPU capacity sum.
> 
> Introduce dl_bw_capacity() which for a symmetric rd w/ a CPU capacity
> of SCHED_CAPACITY_SCALE simply relies on dl_bw_cpus() to return #CPUs
> multiplied by SCHED_CAPACITY_SCALE.
> 
> For an asymmetric rd or a CPU capacity < SCHED_CAPACITY_SCALE it
> computes the CPU capacity sum over rd span and cpu_active_mask.
> 
> A 'XXX Fix:' comment was added to highlight that if 'rq->rd ==
> def_root_domain' AC should be performed against the capacity of the
> CPU the task is running on rather the rd CPU capacity sum. This
> issue already exists w/o capacity awareness.
> 
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> ---
>  kernel/sched/deadline.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 4ae22bfc37ae..ea7282ce484c 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -69,6 +69,34 @@ static inline int dl_bw_cpus(int i)
>  
>  	return cpus;
>  }
> +
> +static inline unsigned long __dl_bw_capacity(int i)
> +{
> +	struct root_domain *rd = cpu_rq(i)->rd;
> +	unsigned long cap = 0;
> +
> +	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
> +			 "sched RCU must be held");
> +
> +	for_each_cpu_and(i, rd->span, cpu_active_mask)
> +		cap += capacity_orig_of(i);
> +
> +	return cap;
> +}
> +
> +/*
> + * XXX Fix: If 'rq->rd == def_root_domain' perform AC against capacity
> + * of the CPU the task is running on rather rd's \Sum CPU capacity.
> + */
> +static inline unsigned long dl_bw_capacity(int i)
> +{
> +	if (!static_branch_unlikely(&sched_asym_cpucapacity) &&
> +	    capacity_orig_of(i) == SCHED_CAPACITY_SCALE) {
> +		return dl_bw_cpus(i) << SCHED_CAPACITY_SHIFT;
> +	} else {
> +		return __dl_bw_capacity(i);
> +	}
> +}
>  #else
>  static inline struct dl_bw *dl_bw_of(int i)
>  {
> @@ -79,6 +107,11 @@ static inline int dl_bw_cpus(int i)
>  {
>  	return 1;
>  }
> +
> +static inline unsigned long dl_bw_capacity(int i)
> +{
> +	return SCHED_CAPACITY_SCALE;
> +}
>  #endif
>  
>  static inline
> -- 

Acked-by: Juri Lelli <juri.lelli@...hat.com>