[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJZ5v0hqRkDmhRBfB4g-2EH2piv-KOQdwad7rVoSK8FzZKg=TA@mail.gmail.com>
Date: Thu, 4 Jan 2024 20:47:19 +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, rafael@...nel.org,
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, mhiramat@...nel.org, qyousef@...alina.io,
wvw@...gle.com
Subject: Re: [PATCH v6 11/23] PM: EM: Add API for updating the runtime
modifiable EM
I don't really like using the API TLA in patch subjects, because it
does not really say much. IMO a subject like this would be better:
"PM: EM: Introduce em_dev_update_perf_domain() for EM updates"
On Thu, Jan 4, 2024 at 6:15 PM Lukasz Luba <lukasz.luba@....com> wrote:
>
> Add API function em_dev_update_perf_domain() which allows to safely
> change the EM.
"... which allows the EM to be changed safely."
New paragraph:
> The concurrent modifiers are protected by the mutex
> to serialize them. Removal of the old memory is asynchronous and
> handled by the RCU mechanisms.
"Concurrent updaters are serialized with a mutex and the removal of
memory that will not be used any more is carried out with the help of
RCU."
>
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
> include/linux/energy_model.h | 8 +++++++
> kernel/power/energy_model.c | 41 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 753d70d0ce7e..f33257ed83fd 100644
> --- a/include/linux/energy_model.h
> +++ b/include/linux/energy_model.h
> @@ -183,6 +183,8 @@ 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_perf_table __rcu *new_table);
> int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
> struct em_data_callback *cb, cpumask_t *span,
> bool microwatts);
> @@ -376,6 +378,12 @@ struct em_perf_table __rcu *em_allocate_table(struct em_perf_domain *pd)
> return NULL;
> }
> static inline void em_free_table(struct em_perf_table __rcu *table) {}
> +static inline
> +int em_dev_update_perf_domain(struct device *dev,
> + struct em_perf_table __rcu *new_table)
> +{
> + return -EINVAL;
> +}
> #endif
>
> #endif
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index bbc406db0be1..496dc00835c6 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -220,6 +220,47 @@ static int em_allocate_perf_table(struct em_perf_domain *pd,
> return 0;
> }
>
> +/**
> + * em_dev_update_perf_domain() - Update runtime EM table for a device
> + * @dev : Device for which the EM is to be updated
> + * @table : The new EM table that is going to be used from now
This is called "new_table" below.
> + *
> + * Update EM runtime modifiable table for the @dev using the provided @table.
> + *
> + * This function uses mutex to serialize writers, so it must not be called
"uses a mutex"
> + * from non-sleeping context.
"a non-sleeping context".
> + *
> + * Return 0 on success or a proper error in case of failure.
It is not clear what "a proper error" means. It would be better to
simply say "or an error code on failure" IMO.
> + */
> +int em_dev_update_perf_domain(struct device *dev,
> + struct em_perf_table __rcu *new_table)
> +{
> + struct em_perf_table __rcu *old_table;
> + struct em_perf_domain *pd;
> +
> + /* Serialize update/unregister or concurrent updates */
> + mutex_lock(&em_pd_mutex);
> +
> + if (!dev || !dev->em_pd) {
dev need not be checked under the lock.
> + mutex_unlock(&em_pd_mutex);
> + return -EINVAL;
> + }
> + pd = dev->em_pd;
> +
> + em_table_inc(new_table);
> +
> + old_table = pd->em_table;
> + rcu_assign_pointer(pd->em_table, new_table);
> +
> + em_cpufreq_update_efficiencies(dev, new_table->state);
> +
> + em_table_dec(old_table);
> +
> + mutex_unlock(&em_pd_mutex);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(em_dev_update_perf_domain);
> +
> static int em_create_runtime_table(struct em_perf_domain *pd)
> {
> struct em_perf_table __rcu *table;
> --
Powered by blists - more mailing lists