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Subject[PATCH 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock
Date
This completely eliminates the contention I am seeing in __cpufreq_cpu_get.
It also nicely stages the lock to be replaced by the rcu.

CC: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
drivers/cpufreq/cpufreq.c | 44 ++++++++++++++++++++++----------------------
1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 1f93dbd..13a83a2 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -45,7 +45,7 @@ static DEFINE_PER_CPU(struct cpufreq_policy *, cpufreq_cpu_data);
/* This one keeps track of the previously set governor of a removed CPU */
static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], cpufreq_cpu_governor);
#endif
-static DEFINE_SPINLOCK(cpufreq_driver_lock);
+static DEFINE_RWLOCK(cpufreq_driver_lock);

/*
* cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure
@@ -149,7 +149,7 @@ static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
goto err_out;

/* get the cpufreq driver */
- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ read_lock_irqsave(&cpufreq_driver_lock, flags);

if (!cpufreq_driver)
goto err_out_unlock;
@@ -167,13 +167,13 @@ static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, bool sysfs)
if (!sysfs && !kobject_get(&data->kobj))
goto err_out_put_module;

- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);
return data;

err_out_put_module:
module_put(cpufreq_driver->owner);
err_out_unlock:
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);
err_out:
return NULL;
}
@@ -751,10 +751,10 @@ static int cpufreq_add_dev_policy(unsigned int cpu,
return -EBUSY;
}

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
cpumask_copy(managed_policy->cpus, policy->cpus);
per_cpu(cpufreq_cpu_data, cpu) = managed_policy;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

pr_debug("CPU already managed, adding link\n");
ret = sysfs_create_link(&dev->kobj,
@@ -850,14 +850,14 @@ static int cpufreq_add_dev_interface(unsigned int cpu,
goto err_out_kobj_put;
}

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
for_each_cpu(j, policy->cpus) {
if (!cpu_online(j))
continue;
per_cpu(cpufreq_cpu_data, j) = policy;
per_cpu(cpufreq_policy_cpu, j) = policy->cpu;
}
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

ret = cpufreq_add_dev_symlink(cpu, policy);
if (ret)
@@ -999,10 +999,10 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)


err_out_unregister:
- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
for_each_cpu(j, policy->cpus)
per_cpu(cpufreq_cpu_data, j) = NULL;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

kobject_put(&policy->kobj);
wait_for_completion(&policy->kobj_unregister);
@@ -1042,11 +1042,11 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif

pr_debug("unregistering CPU %u\n", cpu);

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
data = per_cpu(cpufreq_cpu_data, cpu);

if (!data) {
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);
unlock_policy_rwsem_write(cpu);
return -EINVAL;
}
@@ -1060,7 +1060,7 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
if (unlikely(cpu != data->cpu)) {
pr_debug("removing link\n");
cpumask_clear_cpu(cpu, data->cpus);
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);
kobj = &dev->kobj;
cpufreq_cpu_put(data);
unlock_policy_rwsem_write(cpu);
@@ -1089,7 +1089,7 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
}
}

- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

if (unlikely(cpumask_weight(data->cpus) > 1)) {
for_each_cpu(j, data->cpus) {
@@ -1109,7 +1109,7 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
}
}
#else
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif

if (cpufreq_driver->target)
@@ -1878,13 +1878,13 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
if (driver_data->setpolicy)
driver_data->flags |= CPUFREQ_CONST_LOOPS;

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
if (cpufreq_driver) {
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);
return -EBUSY;
}
cpufreq_driver = driver_data;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

ret = subsys_interface_register(&cpufreq_interface);
if (ret)
@@ -1916,9 +1916,9 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
err_if_unreg:
subsys_interface_unregister(&cpufreq_interface);
err_null_driver:
- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
cpufreq_driver = NULL;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_register_driver);
@@ -1944,9 +1944,9 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
subsys_interface_unregister(&cpufreq_interface);
unregister_hotcpu_notifier(&cpufreq_cpu_notifier);

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);
cpufreq_driver = NULL;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

return 0;
}
--
1.8.0.1


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