Commit cbe5aeed authored by Changwoo Min's avatar Changwoo Min Committed by Rafael J. Wysocki
Browse files

PM: EM: Assign a unique ID when creating a performance domain 



It is necessary to refer to a specific performance domain from a
userspace. For example, the energy model of a particular performance
domain is updated.

To this end, assign a unique ID to each performance domain to address it,
and manage them in a global linked list to look up a specific one by
matching ID. IDA is used for ID assignment, and the mutex is used to
protect the global list from concurrent access.

Note that the mutex (em_pd_list_mutex) is not supposed to hold while
holding em_pd_mutex to avoid ABBA deadlock.

Signed-off-by: default avatarChangwoo Min <changwoo@igalia.com>
Reviewed-by: default avatarLukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20251020220914.320832-2-changwoo@igalia.com


Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 211ddde0

include/linux/energy_model.h

+4 −0
Original line number Diff line number Diff line
@@ -54,6 +54,8 @@ struct em_perf_table { 
/**

 * struct em_perf_domain - Performance domain

 * @em_table:		Pointer to the runtime modifiable em_perf_table

 * @node:		node in	em_pd_list (in energy_model.c)

 * @id:			A unique ID number for each performance domain

 * @nr_perf_states:	Number of performance states

 * @min_perf_state:	Minimum allowed Performance State index

 * @max_perf_state:	Maximum allowed Performance State index
@@ -71,6 +73,8 @@ struct em_perf_table { 
 */

struct em_perf_domain {

	struct em_perf_table __rcu *em_table;

	struct list_head node;

	int id;

	int nr_perf_states;

	int min_perf_state;

	int max_perf_state;

kernel/power/energy_model.c

+29 −1
Original line number Diff line number Diff line
@@ -23,6 +23,16 @@ 
 */

static DEFINE_MUTEX(em_pd_mutex);



/*

 * Manage performance domains with IDs. One can iterate the performance domains

 * through the list and pick one with their associated ID. The mutex serializes

 * the list access. When holding em_pd_list_mutex, em_pd_mutex should not be

 * taken to avoid potential deadlock.

 */

static DEFINE_IDA(em_pd_ida);

static LIST_HEAD(em_pd_list);

static DEFINE_MUTEX(em_pd_list_mutex);



static void em_cpufreq_update_efficiencies(struct device *dev,

					   struct em_perf_state *table);

static void em_check_capacity_update(void);
@@ -396,7 +406,7 @@ static int em_create_pd(struct device *dev, int nr_states, 
	struct em_perf_table *em_table;

	struct em_perf_domain *pd;

	struct device *cpu_dev;

	int cpu, ret, num_cpus;

	int cpu, ret, num_cpus, id;



	if (_is_cpu_device(dev)) {

		num_cpus = cpumask_weight(cpus);
@@ -420,6 +430,13 @@ static int em_create_pd(struct device *dev, int nr_states, 


	pd->nr_perf_states = nr_states;



	INIT_LIST_HEAD(&pd->node);



	id = ida_alloc(&em_pd_ida, GFP_KERNEL);

	if (id < 0)

		return -ENOMEM;

	pd->id = id;



	em_table = em_table_alloc(pd);

	if (!em_table)

		goto free_pd;
@@ -444,6 +461,7 @@ static int em_create_pd(struct device *dev, int nr_states, 
	kfree(em_table);

free_pd:

	kfree(pd);

	ida_free(&em_pd_ida, id);

	return -EINVAL;

}
@@ -660,6 +678,10 @@ int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states, 
unlock:

	mutex_unlock(&em_pd_mutex);



	mutex_lock(&em_pd_list_mutex);

	list_add_tail(&dev->em_pd->node, &em_pd_list);

	mutex_unlock(&em_pd_list_mutex);



	return ret;

}

EXPORT_SYMBOL_GPL(em_dev_register_pd_no_update);
@@ -678,6 +700,10 @@ void em_dev_unregister_perf_domain(struct device *dev) 
	if (_is_cpu_device(dev))

		return;



	mutex_lock(&em_pd_list_mutex);

	list_del_init(&dev->em_pd->node);

	mutex_unlock(&em_pd_list_mutex);



	/*

	 * The mutex separates all register/unregister requests and protects

	 * from potential clean-up/setup issues in the debugfs directories.
@@ -689,6 +715,8 @@ void em_dev_unregister_perf_domain(struct device *dev) 
	em_table_free(rcu_dereference_protected(dev->em_pd->em_table,

						lockdep_is_held(&em_pd_mutex)));



	ida_free(&em_pd_ida, dev->em_pd->id);



	kfree(dev->em_pd);

	dev->em_pd = NULL;

	mutex_unlock(&em_pd_mutex);