Re: [PATCH v5 10/23] PM: EM: Add API for memory allocations for new tables

Qais Yousef
2023-12-17T17:59:57Z

On 11/29/23 11:08, Lukasz Luba 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@arm.com>
> ---
> include/linux/energy_model.h | 11 +++++++++
> kernel/power/energy_model.c | 44 ++++++++++++++++++++++++++++++++++--
> 2 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> index 94a77a813724..e785211828fe 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
> * @state: List of performance states, in ascending order
> */
> struct em_perf_table {
> struct rcu_head rcu;
> + struct kref refcount;
> 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
> @@ -368,6 +373,12 @@ 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 489287666705..489a358b9a00 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(runtime_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_inc_usage(struct em_perf_table __rcu *table)
> +{
> + kref_get(&table->refcount);
> +}
> +
> +static void em_dec_usage(struct em_perf_table __rcu *table)
> +{
> + kref_put(&table->refcount, em_release_table_kref);
> +}

nit: em_table_inc/dec() instead? matches general theme elsewhere in the code
base.

> +
> +/**
> + * 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_dec_usage(table);
> +}
> +
> +/**
> + * em_allocate_table() - Handles safe allocation of the new EM table
> + * @table : EM memory which is going to be freed
> + *
> + * Increments the reference counter to mark that there is an owner of that
> + * 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 +162,12 @@ 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;
> +
> + kref_init(&table->refcount);
> + em_inc_usage(table);

Doesn't kref_init() initialize to the count to 1 already? Is the em_inc_usage()
needed here?

Cheers

--
Qais Yousef

> +
> return table;
> }
>
> --
> 2.25.1
>