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Subject[PATCH v3 1/2] cpufreq: Convert the cpufreq_driver_lock to a rwlock
Date
This eliminates the contention I am seeing in __cpufreq_cpu_get.
It also nicely stages the lock to be replaced by the rcu.

Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
drivers/cpufreq/cpufreq.c | 52 +++++++++++++++++++++++------------------------
1 file changed, 26 insertions(+), 26 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index b02824d..c5996fe 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
@@ -137,7 +137,7 @@ 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;
@@ -155,13 +155,13 @@ 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;
}
@@ -266,9 +266,9 @@ void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
pr_debug("notification %u of frequency transition to %u kHz\n",
state, freqs->new);

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ read_lock_irqsave(&cpufreq_driver_lock, flags);
policy = per_cpu(cpufreq_cpu_data, freqs->cpu);
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);

switch (state) {

@@ -765,12 +765,12 @@ 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) {
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)
@@ -813,12 +813,12 @@ static int cpufreq_add_policy_cpu(unsigned int cpu, unsigned int sibling,

lock_policy_rwsem_write(sibling);

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);

cpumask_set_cpu(cpu, policy->cpus);
per_cpu(cpufreq_policy_cpu, cpu) = policy->cpu;
per_cpu(cpufreq_cpu_data, cpu) = policy;
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ write_unlock_irqrestore(&cpufreq_driver_lock, flags);

unlock_policy_rwsem_write(sibling);

@@ -871,15 +871,15 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)

#ifdef CONFIG_HOTPLUG_CPU
/* Check if this cpu was hot-unplugged earlier and has siblings */
- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ read_lock_irqsave(&cpufreq_driver_lock, flags);
for_each_online_cpu(sibling) {
struct cpufreq_policy *cp = per_cpu(cpufreq_cpu_data, sibling);
if (cp && cpumask_test_cpu(cpu, cp->related_cpus)) {
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);
return cpufreq_add_policy_cpu(cpu, sibling, dev);
}
}
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);
#endif
#endif

@@ -952,10 +952,10 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
return 0;

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);
@@ -1008,12 +1008,12 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif

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

- spin_lock_irqsave(&cpufreq_driver_lock, flags);
+ write_lock_irqsave(&cpufreq_driver_lock, flags);

data = per_cpu(cpufreq_cpu_data, cpu);
per_cpu(cpufreq_cpu_data, cpu) = NULL;

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

if (!data) {
pr_debug("%s: No cpu_data found\n", __func__);
@@ -1047,9 +1047,9 @@ static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif
WARN_ON(lock_policy_rwsem_write(cpu));
cpumask_set_cpu(cpu, data->cpus);

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

unlock_policy_rwsem_write(cpu);

@@ -1848,13 +1848,13 @@ 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)
@@ -1886,9 +1886,9 @@ 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);
@@ -1914,9 +1914,9 @@ 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;
}
--
1.8.1.2


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