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Message-ID: <CAJZ5v0gzQhw3wkRVFTEx-y4pawknJqC2JPrN6_dqd77vTVuSOw@mail.gmail.com>
Date: Tue, 29 Oct 2024 19:29:31 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	dietmar.eggemann@....com, rafael@...nel.org
Subject: Re: [PATCH v2 1/1] PM: EM: Add min/max available performance state limits

On Tue, Oct 29, 2024 at 10:43 AM Lukasz Luba <lukasz.luba@....com> wrote:
>
> On some devices there are HW dependencies for shared frequency and voltage
> between devices. It will impact Energy Aware Scheduler (EAS) decision,
> where CPUs share the voltage & frequency domain with other CPUs or devices
> e.g.
> - Mid CPUs + Big CPU
> - Little CPU + L3 cache in DSU
> - some other device + Little CPUs
>
> Detailed explanation of one example:
> When the L3 cache frequency is increased, the affected Little CPUs might
> run at higher voltage and frequency. That higher voltage causes higher CPU
> power and thus more energy is used for running the tasks. This is
> important for background running tasks, which try to run on energy
> efficient CPUs.
>
> Therefore, add performance state limits which are applied for the device
> (in this case CPU). This is important on SoCs with HW dependencies
> mentioned above so that the Energy Aware Scheduler (EAS) does not use
> performance states outside the valid min-max range for energy calculation.
>
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  include/linux/energy_model.h | 24 ++++++++++++++---
>  kernel/power/energy_model.c  | 52 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 1ff52020cf757..e83bf230e18d1 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -55,6 +55,8 @@ struct em_perf_table {
>   * struct em_perf_domain - Performance domain
>   * @em_table:          Pointer to the runtime modifiable em_perf_table
>   * @nr_perf_states:    Number of performance states
> + * @min_ps:            Minimum allowed Performance State index
> + * @max_ps:            Maximum allowed Performance State index
>   * @flags:             See "em_perf_domain flags"
>   * @cpus:              Cpumask covering the CPUs of the domain. It's here
>   *                     for performance reasons to avoid potential cache
> @@ -70,6 +72,8 @@ struct em_perf_table {
>  struct em_perf_domain {
>         struct em_perf_table __rcu *em_table;
>         int nr_perf_states;
> +       int min_ps;
> +       int max_ps;
>         unsigned long flags;
>         unsigned long cpus[];
>  };
> @@ -173,6 +177,8 @@ void em_table_free(struct em_perf_table __rcu *table);
>  int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
>                          int nr_states);
>  int em_dev_update_chip_binning(struct device *dev);
> +int em_update_performance_limits(struct em_perf_domain *pd,
> +               unsigned long freq_min_khz, unsigned long freq_max_khz);
>
>  /**
>   * em_pd_get_efficient_state() - Get an efficient performance state from the EM
> @@ -180,6 +186,8 @@ int em_dev_update_chip_binning(struct device *dev);
>   * @nr_perf_states:    Number of performance states
>   * @max_util:          Max utilization to map with the EM
>   * @pd_flags:          Performance Domain flags
> + * @min_ps:            Minimum allowed Performance State index
> + * @max_ps:            Maximum allowed Performance State index
>   *
>   * It is called from the scheduler code quite frequently and as a consequence
>   * doesn't implement any check.
> @@ -189,12 +197,13 @@ int em_dev_update_chip_binning(struct device *dev);
>   */
>  static inline int
>  em_pd_get_efficient_state(struct em_perf_state *table, int nr_perf_states,
> -                         unsigned long max_util, unsigned long pd_flags)
> +                         unsigned long max_util, unsigned long pd_flags,
> +                         int min_ps, int max_ps)
>  {
>         struct em_perf_state *ps;
>         int i;
>
> -       for (i = 0; i < nr_perf_states; i++) {
> +       for (i = min_ps; i <= max_ps; i++) {
>                 ps = &table[i];
>                 if (ps->performance >= max_util) {
>                         if (pd_flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
> @@ -204,7 +213,7 @@ em_pd_get_efficient_state(struct em_perf_state *table, int nr_perf_states,
>                 }
>         }
>
> -       return nr_perf_states - 1;
> +       return max_ps;
>  }
>
>  /**
> @@ -254,7 +263,8 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>          */
>         em_table = rcu_dereference(pd->em_table);
>         i = em_pd_get_efficient_state(em_table->state, pd->nr_perf_states,
> -                                     max_util, pd->flags);
> +                                     max_util, pd->flags, pd->min_ps,
> +                                     pd->max_ps);
>         ps = &em_table->state[i];
>
>         /*
> @@ -391,6 +401,12 @@ static inline int em_dev_update_chip_binning(struct device *dev)
>  {
>         return -EINVAL;
>  }
> +static inline
> +int em_update_performance_limits(struct em_perf_domain *pd,
> +               unsigned long freq_min_khz, unsigned long freq_max_khz)
> +{
> +       return -EINVAL;
> +}
>  #endif
>
>  #endif
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 927cc55ba0b3d..436c2b8fdf9eb 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -628,6 +628,8 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>                 goto unlock;
>
>         dev->em_pd->flags |= flags;
> +       dev->em_pd->min_ps = 0;
> +       dev->em_pd->max_ps = nr_states - 1;
>
>         em_cpufreq_update_efficiencies(dev, dev->em_pd->em_table->state);
>
> @@ -856,3 +858,53 @@ int em_dev_update_chip_binning(struct device *dev)
>         return em_recalc_and_update(dev, pd, em_table);
>  }
>  EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);
> +
> +
> +/**
> + * em_update_performance_limits() - Update Energy Model with performance
> + *                             limits information.
> + * @pd                 : Performance Domain with EM that has to be updated.
> + * @freq_min_khz       : New minimum allowed frequency for this device.
> + * @freq_max_khz       : New maximum allowed frequency for this device.
> + *
> + * This function allows to update the EM with information about available
> + * performance levels. It takes the minimum and maximum frequency in kHz
> + * and does internal translation to performance levels.
> + * Returns 0 on success or -EINVAL when failed.
> + */
> +int em_update_performance_limits(struct em_perf_domain *pd,
> +               unsigned long freq_min_khz, unsigned long freq_max_khz)
> +{
> +       struct em_perf_state *table;
> +       int min_ps = -1;
> +       int max_ps = -1;
> +       int i;
> +
> +       if (!pd)
> +               return -EINVAL;
> +
> +       rcu_read_lock();
> +       table = em_perf_state_from_pd(pd);
> +
> +       for (i = 0; i < pd->nr_perf_states; i++) {
> +               if (freq_min_khz == table[i].frequency)
> +                       min_ps = i;
> +               if (freq_max_khz == table[i].frequency)
> +                       max_ps = i;
> +       }
> +       rcu_read_unlock();
> +
> +       /* Only update when both are found and sane */
> +       if (min_ps < 0 || max_ps < 0 || max_ps < min_ps)
> +               return -EINVAL;
> +
> +
> +       /* Guard simultaneous updates and make them atomic */
> +       mutex_lock(&em_pd_mutex);
> +       pd->min_ps = min_ps;
> +       pd->max_ps = max_ps;
> +       mutex_unlock(&em_pd_mutex);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(em_update_performance_limits);

It would be good to have at least one caller of this function in the tree.

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