Commit 285189c5 authored by Liao Chang's avatar Liao Chang Committed by Rafael J. Wysocki
Browse files

cpufreq: userspace: Use fine-grained mutex in userspace governor 



The userspace governor currently uses a big global mutex to avoid the
race condition on the governor_data field of cpufreq_policy structure.

This leads to a low concurrency if multiple userspace applications are
trying to set the speed of different policies at the same time.

Introduce a per-policy mutex to allow the updating of different policies
to be performed concurrently, improving overall concurrency.

Signed-off-by: default avatarLiao Chang <liaochang1@huawei.com>
Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 842c34a2

drivers/cpufreq/cpufreq_userspace.c

+40 −29
Original line number Diff line number Diff line
@@ -16,7 +16,11 @@ 
#include <linux/slab.h>



static DEFINE_PER_CPU(unsigned int, cpu_is_managed);

static DEFINE_MUTEX(userspace_mutex);



struct userspace_policy {

	unsigned int setspeed;

	struct mutex mutex;

};



/**

 * cpufreq_set - set the CPU frequency
@@ -28,19 +32,19 @@ static DEFINE_MUTEX(userspace_mutex); 
static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq)

{

	int ret = -EINVAL;

	unsigned int *setspeed = policy->governor_data;

	struct userspace_policy *userspace = policy->governor_data;



	pr_debug("cpufreq_set for cpu %u, freq %u kHz\n", policy->cpu, freq);



	mutex_lock(&userspace_mutex);

	mutex_lock(&userspace->mutex);

	if (!per_cpu(cpu_is_managed, policy->cpu))

		goto err;



	*setspeed = freq;

	userspace->setspeed = freq;



	ret = __cpufreq_driver_target(policy, freq, CPUFREQ_RELATION_L);

 err:

	mutex_unlock(&userspace_mutex);

	mutex_unlock(&userspace->mutex);

	return ret;

}
@@ -51,67 +55,74 @@ static ssize_t show_speed(struct cpufreq_policy *policy, char *buf) 


static int cpufreq_userspace_policy_init(struct cpufreq_policy *policy)

{

	unsigned int *setspeed;

	struct userspace_policy *userspace;



	setspeed = kzalloc(sizeof(*setspeed), GFP_KERNEL);

	if (!setspeed)

	userspace = kzalloc(sizeof(*userspace), GFP_KERNEL);

	if (!userspace)

		return -ENOMEM;



	policy->governor_data = setspeed;

	mutex_init(&userspace->mutex);



	policy->governor_data = userspace;

	return 0;

}



/*

 * Any routine that writes to the policy struct will hold the "rwsem" of

 * policy struct that means it is free to free "governor_data" here.

 */

static void cpufreq_userspace_policy_exit(struct cpufreq_policy *policy)

{

	mutex_lock(&userspace_mutex);

	kfree(policy->governor_data);

	policy->governor_data = NULL;

	mutex_unlock(&userspace_mutex);

}



static int cpufreq_userspace_policy_start(struct cpufreq_policy *policy)

{

	unsigned int *setspeed = policy->governor_data;

	struct userspace_policy *userspace = policy->governor_data;



	BUG_ON(!policy->cur);

	pr_debug("started managing cpu %u\n", policy->cpu);



	mutex_lock(&userspace_mutex);

	mutex_lock(&userspace->mutex);

	per_cpu(cpu_is_managed, policy->cpu) = 1;

	*setspeed = policy->cur;

	mutex_unlock(&userspace_mutex);

	userspace->setspeed = policy->cur;

	mutex_unlock(&userspace->mutex);

	return 0;

}



static void cpufreq_userspace_policy_stop(struct cpufreq_policy *policy)

{

	unsigned int *setspeed = policy->governor_data;

	struct userspace_policy *userspace = policy->governor_data;



	pr_debug("managing cpu %u stopped\n", policy->cpu);



	mutex_lock(&userspace_mutex);

	mutex_lock(&userspace->mutex);

	per_cpu(cpu_is_managed, policy->cpu) = 0;

	*setspeed = 0;

	mutex_unlock(&userspace_mutex);

	userspace->setspeed = 0;

	mutex_unlock(&userspace->mutex);

}



static void cpufreq_userspace_policy_limits(struct cpufreq_policy *policy)

{

	unsigned int *setspeed = policy->governor_data;

	struct userspace_policy *userspace = policy->governor_data;



	mutex_lock(&userspace_mutex);

	mutex_lock(&userspace->mutex);



	pr_debug("limit event for cpu %u: %u - %u kHz, currently %u kHz, last set to %u kHz\n",

		 policy->cpu, policy->min, policy->max, policy->cur, *setspeed);



	if (policy->max < *setspeed)

		__cpufreq_driver_target(policy, policy->max, CPUFREQ_RELATION_H);

	else if (policy->min > *setspeed)

		__cpufreq_driver_target(policy, policy->min, CPUFREQ_RELATION_L);

		 policy->cpu, policy->min, policy->max, policy->cur, userspace->setspeed);



	if (policy->max < userspace->setspeed)

		__cpufreq_driver_target(policy, policy->max,

					CPUFREQ_RELATION_H);

	else if (policy->min > userspace->setspeed)

		__cpufreq_driver_target(policy, policy->min,

					CPUFREQ_RELATION_L);

	else

		__cpufreq_driver_target(policy, *setspeed, CPUFREQ_RELATION_L);

		__cpufreq_driver_target(policy, userspace->setspeed,

					CPUFREQ_RELATION_L);



	mutex_unlock(&userspace_mutex);

	mutex_unlock(&userspace->mutex);

}



static struct cpufreq_governor cpufreq_gov_userspace = {