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: Liao Chang <liaochang1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/cpufreq_userspace.c b/drivers/cpufreq/cpufreq_userspace.c
index 50a4d784658009112d1d160e8b3bc8d9d9f2de0d..442e31060d6275efbffea654bc9d053c9b922c59 100644 (file)
--- a/drivers/cpufreq/cpufreq_userspace.c
+++ b/drivers/cpufreq/cpufreq_userspace.c
@@ -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 = {