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Date: Wed, 10 Jan 2024 14:09:38 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.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 10/23] PM: EM: Add API for memory allocations for new
tables
On 1/4/24 19:35, Rafael J. Wysocki wrote:
> On Thu, Jan 4, 2024 at 6:15 PM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> The runtime modified EM table can be provided from drivers. Create
>> mechanism which allows safely allocate and free the table for device
>> drivers. The same table can be used by the EAS in task scheduler code
>> paths, so make sure the memory is not freed when the device driver module
>> is unloaded.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>> include/linux/energy_model.h | 11 +++++++++
>> kernel/power/energy_model.c | 43 ++++++++++++++++++++++++++++++++++--
>> 2 files changed, 52 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
>> index 5f842da3bb0c..753d70d0ce7e 100644
>> --- a/include/linux/energy_model.h
>> +++ b/include/linux/energy_model.h
>> @@ -5,6 +5,7 @@
>> #include <linux/device.h>
>> #include <linux/jump_label.h>
>> #include <linux/kobject.h>
>> +#include <linux/kref.h>
>> #include <linux/rcupdate.h>
>> #include <linux/sched/cpufreq.h>
>> #include <linux/sched/topology.h>
>> @@ -39,10 +40,12 @@ struct em_perf_state {
>> /**
>> * struct em_perf_table - Performance states table
>> * @rcu: RCU used for safe access and destruction
>> + * @refcount: Reference count to track the owners
>
> "Reference counter to track the users"
>
> Also it is not really just a counter - it provides the memory release
> mechanism too.
Agree
>
>> * @state: List of performance states, in ascending order
>> */
>> struct em_perf_table {
>> struct rcu_head rcu;
>> + struct kref refcount;
>
> So I would just call it kref.
OK
>
>> struct em_perf_state state[];
>> };
>>
>> @@ -184,6 +187,8 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>> struct em_data_callback *cb, cpumask_t *span,
>> bool microwatts);
>> void em_dev_unregister_perf_domain(struct device *dev);
>> +struct em_perf_table __rcu *em_allocate_table(struct em_perf_domain *pd);
>> +void em_free_table(struct em_perf_table __rcu *table);
>>
>> /**
>> * em_pd_get_efficient_state() - Get an efficient performance state from the EM
>> @@ -365,6 +370,12 @@ static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
>> {
>> return 0;
>> }
>> +static inline
>> +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) {}
>> #endif
>>
>> #endif
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index c03010084208..bbc406db0be1 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -114,12 +114,46 @@ static void em_destroy_table_rcu(struct rcu_head *rp)
>> kfree(table);
>> }
>>
>> -static void em_free_table(struct em_perf_table __rcu *table)
>> +static void em_release_table_kref(struct kref *kref)
>> {
>> + struct em_perf_table __rcu *table;
>> +
>> + /* It was the last owner of this table so we can free */
>> + table = container_of(kref, struct em_perf_table, refcount);
>> +
>> call_rcu(&table->rcu, em_destroy_table_rcu);
>> }
>>
>> -static struct em_perf_table __rcu *
>> +static inline void em_table_inc(struct em_perf_table __rcu *table)
>
> Why not em_table_get()?
I will change that...
>
>> +{
>> + kref_get(&table->refcount);
>> +}
>> +
>> +static void em_table_dec(struct em_perf_table __rcu *table)
>
> And em_table_put() here?
and this as well.
>
> Note that I do realize that the "put" and "get" terminology is used in
> one of the subsequent patches - I'll get to it later.
>
>> +{
>> + kref_put(&table->refcount, em_release_table_kref);
>> +}
>> +
>> +/**
>> + * em_free_table() - Handles safe free of the EM table when needed
>> + * @table : EM memory which is going to be freed
>> + *
>> + * No return values.
>> + */
>> +void em_free_table(struct em_perf_table __rcu *table)
>> +{
>> + em_table_dec(table);
>> +}
>
> Why is this necessary? The function called by it could be extern
> instead and wrapped into a static inline wrapper in a header (if you
> really need the alias).
Sounds good, I'll change it.
>
>> +
>> +/**
>> + * em_allocate_table() - Handles safe allocation of the new EM table
>
> " - Allocate a new EM table"
OK
>
> And I would call this em_table_alloc() and (maybe) add an
> em_table_free() alias for em_table_put().
OK
>
>> + * @table : EM memory which is going to be freed
>
> So the argument is called "pd" and it is not a table. It is also used
> for computing the size of the new table AFAICS.
True, good catch.
>
>> + *
>> + * Increments the reference counter to mark that there is an owner of that
>
> "Allocate a new EM table and initialize its kref to indicate that it
> has a user."
OK
>
>> + * EM table. That might be a device driver module or EAS.
>> + * Returns allocated table or error.
>> + */
>> +struct em_perf_table __rcu *
>> em_allocate_table(struct em_perf_domain *pd)
>> {
>> struct em_perf_table __rcu *table;
>> @@ -128,6 +162,11 @@ em_allocate_table(struct em_perf_domain *pd)
>> table_size = sizeof(struct em_perf_state) * pd->nr_perf_states;
>>
>> table = kzalloc(sizeof(*table) + table_size, GFP_KERNEL);
>> + if (!table)
>> + return table;
>
> I would return NULL from here explicitly.
OK
>
>> +
>> + kref_init(&table->refcount);
>> +
>> return table;
>> }
>>
>> --
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