linux-kernel - Re: [PATCH 1/4] sched/topology: Store root domain CPU capacity sum

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Date:   Wed, 8 Apr 2020 14:29:16 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        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 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] sched/topology: Store root domain CPU capacity sum

On Wed, 8 Apr 2020 at 11:50, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> Add the sum of (original) CPU capacity of all member CPUs to the root
> domain.
>
> This is needed for capacity-aware SCHED_DEADLINE admission control.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> ---
>  kernel/sched/sched.h    | 11 +++++++++++
>  kernel/sched/topology.c | 14 ++++++++++----
>  2 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 1e72d1b3d3ce..91bd0cb0c529 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -797,6 +797,7 @@ struct root_domain {
>         cpumask_var_t           rto_mask;
>         struct cpupri           cpupri;
>
> +       unsigned long           sum_cpu_capacity;
>         unsigned long           max_cpu_capacity;
>
>         /*
> @@ -2393,6 +2394,16 @@ static inline unsigned long capacity_orig_of(int cpu)
>  {
>         return cpu_rq(cpu)->cpu_capacity_orig;
>  }
> +
> +static inline unsigned long rd_capacity(int cpu)
> +{
> +       return cpu_rq(cpu)->rd->sum_cpu_capacity;
> +}
> +#else
> +static inline unsigned long rd_capacity(int cpu)
> +{
> +       return SCHED_CAPACITY_SCALE;
> +}
>  #endif
>
>  /**
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 8344757bba6e..74b0c0fa4b1b 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -2052,12 +2052,17 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
>         /* Attach the domains */
>         rcu_read_lock();
>         for_each_cpu(i, cpu_map) {
> +               unsigned long cap = arch_scale_cpu_capacity(i);

Why do you replace the use of rq->cpu_capacity_orig by
arch_scale_cpu_capacity(i) ?
There is nothing about this change in the commit message

> +
>                 rq = cpu_rq(i);
>                 sd = *per_cpu_ptr(d.sd, i);
>
>                 /* Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing: */
> -               if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))
> -                       WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);
> +               if (cap > READ_ONCE(d.rd->max_cpu_capacity))
> +                       WRITE_ONCE(d.rd->max_cpu_capacity, cap);
> +
> +               WRITE_ONCE(d.rd->sum_cpu_capacity,
> +                          READ_ONCE(d.rd->sum_cpu_capacity) + cap);
>
>                 cpu_attach_domain(sd, d.rd, i);
>         }
> @@ -2067,8 +2072,9 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
>                 static_branch_inc_cpuslocked(&sched_asym_cpucapacity);
>
>         if (rq && sched_debug_enabled) {
> -               pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
> -                       cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
> +               pr_info("root domain span: %*pbl (capacity = %lu max cpu_capacity = %lu)\n",
> +                       cpumask_pr_args(cpu_map), rq->rd->sum_cpu_capacity,
> +                       rq->rd->max_cpu_capacity);
>         }
>
>         ret = 0;
> --
> 2.17.1
>