linux-kernel - Re: [PATCH 10/17] PM: EM: Add runtime update interface to modify EM power

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Date:   Tue, 11 Apr 2023 17:40:20 +0200
From:   Pierre Gondois <pierre.gondois@....com>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, rafael@...nel.org
Cc:     dietmar.eggemann@....com, rui.zhang@...el.com,
        amit.kucheria@...durent.com, amit.kachhap@...il.com,
        daniel.lezcano@...aro.org, viresh.kumar@...aro.org,
        len.brown@...el.com, pavel@....cz, ionela.voinescu@....com,
        rostedt@...dmis.org, mhiramat@...nel.org
Subject: Re: [PATCH 10/17] PM: EM: Add runtime update interface to modify EM
 power

Hello Lukasz,

On 3/14/23 11:33, Lukasz Luba wrote:
> Add an interface which allows to modify EM power data at runtime.
> The new power information is populated by the provided callback, which
> is called for each performance state. The CPU frequencies' efficiency is
> re-calculated since that might be affected as well. The old EM memory
> is going to be freed later using RCU mechanism.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>   include/linux/energy_model.h |   8 +++
>   kernel/power/energy_model.c  | 109 +++++++++++++++++++++++++++++++++++
>   2 files changed, 117 insertions(+)
> 
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index a616006a8130..e1772aa6c843 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -202,6 +202,8 @@ struct em_data_callback {
>   
>   struct em_perf_domain *em_cpu_get(int cpu);
>   struct em_perf_domain *em_pd_get(struct device *dev);
> +int em_dev_update_perf_domain(struct device *dev, struct em_data_callback *cb,
> +			      void *priv);
>   int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>   				struct em_data_callback *cb, cpumask_t *span,
>   				bool microwatts);
> @@ -382,6 +384,12 @@ static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
>   {
>   	return 0;
>   }
> +static inline
> +int em_dev_update_perf_domain(struct device *dev, struct em_data_callback *cb,
> +			      void *priv)
> +{
> +	return -EINVAL;
> +}
>   #endif
>   
>   #endif
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 87962b877376..e0e8fba3d02b 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c

[snip]

> @@ -531,9 +628,21 @@ void em_dev_unregister_perf_domain(struct device *dev)
>   
>   	tmp = pd->runtime_table;
>   
> +	/*
> +	 * Safely destroy runtime modifiable EM. By using the call
> +	 * synchronize_rcu() we make sure we don't progress till last user
> +	 * finished the RCU section and our update got applied.
> +	 */
>   	rcu_assign_pointer(pd->runtime_table, NULL);
>   	synchronize_rcu();
>   
> +	/*
> +	 * After the sync no updates will be in-flight, so free the old
> +	 * memory.
> +	 */
> +	if (tmp->state != pd->table)
> +		kfree(tmp->state);
> +

NIT: I think that the call 'kfree(pd->default_table->state)' which is done in
the patch:
   PM: EM: Refactor struct em_perf_domain and add default_table
should be done here, otherwise this bit of memory is not freed.

Regards,
Pierre


>   	kfree(tmp);
>   
>   	kfree(dev->em_pd->table);