Re: [PATCH v4 12/18] PM: EM: Use runtime modified EM for CPUs energy estimation in EAS

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <lukasz.luba@arm.com> wrote:
>
> The new Energy Model (EM) supports runtime modification of the performance
> state table to better model the power used by the SoC. Use this new
> feature to improve energy estimation and therefore task placement in
> Energy Aware Scheduler (EAS).
>
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  include/linux/energy_model.h | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 8f055ab356ed..41290ee2cdd0 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -261,15 +261,14 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>                                 unsigned long max_util, unsigned long sum_util,
>                                 unsigned long allowed_cpu_cap)
>  {
> +       struct em_perf_table *runtime_table;

You may as well call it just "table".  The "runtime_" prefix doesn't
add much value here IMO.

>         unsigned long freq, scale_cpu;
> -       struct em_perf_state *table, *ps;
> +       struct em_perf_state *ps;
>         int cpu, i;
>
>         if (!sum_util)
>                 return 0;
>
> -       table = pd->default_table->state;
> -
>         /*
>          * In order to predict the performance state, map the utilization of
>          * the most utilized CPU of the performance domain to a requested
> @@ -280,7 +279,14 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>          */
>         cpu = cpumask_first(to_cpumask(pd->cpus));
>         scale_cpu = arch_scale_cpu_capacity(cpu);
> -       ps = &table[pd->nr_perf_states - 1];
> +
> +       /*
> +        * No rcu_read_lock() since it's already called by task scheduler.
> +        * The runtime_table is always there for CPUs, so we don't check.
> +        */
> +       runtime_table = rcu_dereference(pd->runtime_table);
> +
> +       ps = &runtime_table->state[pd->nr_perf_states - 1];
>
>         max_util = map_util_perf(max_util);
>         max_util = min(max_util, allowed_cpu_cap);
> @@ -290,9 +296,9 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>          * Find the lowest performance state of the Energy Model above the
>          * requested frequency.
>          */
> -       i = em_pd_get_efficient_state(table, pd->nr_perf_states, freq,
> -                                     pd->flags);
> -       ps = &table[i];
> +       i = em_pd_get_efficient_state(runtime_table->state, pd->nr_perf_states,
> +                                     freq, pd->flags);
> +       ps = &runtime_table->state[i];
>
>         /*
>          * The capacity of a CPU in the domain at the performance state (ps)
> --