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Subject[PATCH v4 3/5] cpufreq: Don't destroy/realloc policy/sysfs on hotplug/suspend
Date
This patch simplifies a lot of the hotplug/suspend code by not
adding/removing/moving the policy/sysfs/kobj during hotplug and just leaves
the cpufreq directory and policy in place irrespective of whether the CPUs
are ONLINE/OFFLINE.

Leaving the policy, sysfs and kobject in place also brings these additional
benefits:
* Faster suspend/resume
* Faster hotplug
* Sysfs file permissions maintained across hotplug
* Policy settings and governor tunables maintained across hotplug
* Cpufreq stats would be maintained across hotplug for all CPUs and can be
queried even after CPU goes OFFLINE

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
---
drivers/cpufreq/cpufreq.c | 83 ++++++++++++++++-------------------------------
1 file changed, 28 insertions(+), 55 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index af4f291..d9fc6e5 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -865,7 +865,7 @@ static int cpufreq_add_dev_symlink(struct cpufreq_policy *policy)
unsigned int j;
int ret = 0;

- for_each_cpu(j, policy->cpus) {
+ for_each_cpu(j, policy->related_cpus) {
struct device *cpu_dev;

if (j == policy->kobj_cpu)
@@ -968,7 +968,7 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy *policy,
int ret = 0;
unsigned long flags;

- if (has_target()) {
+ if (cpumask_weight(policy->cpus) && has_target()) {
ret = __cpufreq_governor(policy, CPUFREQ_GOV_STOP);
if (ret) {
pr_err("%s: Failed to stop governor\n", __func__);
@@ -997,7 +997,7 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy *policy,
}
}

- return sysfs_create_link(&dev->kobj, &policy->kobj, "cpufreq");
+ return 0;
}
#endif

@@ -1100,9 +1100,6 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
struct cpufreq_policy *policy;
unsigned long flags;
bool recover_policy = cpufreq_suspended;
-#ifdef CONFIG_HOTPLUG_CPU
- struct cpufreq_policy *tpolicy;
-#endif

if (cpu_is_offline(cpu))
return 0;
@@ -1113,28 +1110,22 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
/* check whether a different CPU already registered this
* CPU because it is in the same boat. */
policy = cpufreq_cpu_get(cpu);
- if (unlikely(policy)) {
+ if (policy) {
+ if (!cpumask_test_cpu(cpu, policy->cpus))
+ ret = cpufreq_add_policy_cpu(policy, cpu, dev);
+ else
+ ret = 0;
cpufreq_cpu_put(policy);
- return 0;
+ return ret;
}
#endif

if (!down_read_trylock(&cpufreq_rwsem))
return 0;

-#ifdef CONFIG_HOTPLUG_CPU
- /* Check if this cpu was hot-unplugged earlier and has siblings */
- read_lock_irqsave(&cpufreq_driver_lock, flags);
- list_for_each_entry(tpolicy, &cpufreq_policy_list, policy_list) {
- if (cpumask_test_cpu(cpu, tpolicy->related_cpus)) {
- read_unlock_irqrestore(&cpufreq_driver_lock, flags);
- ret = cpufreq_add_policy_cpu(tpolicy, cpu, dev);
- up_read(&cpufreq_rwsem);
- return ret;
- }
- }
- read_unlock_irqrestore(&cpufreq_driver_lock, flags);
-#endif
+ /* If we get this far, this is the first time we are adding the
+ * policy */
+ recover_policy = false;

/*
* Restore the saved policy when doing light-weight init and fall back
@@ -1189,7 +1180,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)

down_write(&policy->rwsem);
write_lock_irqsave(&cpufreq_driver_lock, flags);
- for_each_cpu(j, policy->cpus)
+ for_each_cpu(j, policy->related_cpus)
per_cpu(cpufreq_cpu_data, j) = policy;
write_unlock_irqrestore(&cpufreq_driver_lock, flags);

@@ -1274,7 +1265,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
err_out_unregister:
err_get_freq:
write_lock_irqsave(&cpufreq_driver_lock, flags);
- for_each_cpu(j, policy->cpus)
+ for_each_cpu(j, policy->related_cpus)
per_cpu(cpufreq_cpu_data, j) = NULL;
write_unlock_irqrestore(&cpufreq_driver_lock, flags);

@@ -1340,21 +1331,15 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
struct subsys_interface *sif)
{
unsigned int cpu = dev->id, cpus;
- int new_cpu, ret;
+ int new_cpu, ret = 0;
unsigned long flags;
struct cpufreq_policy *policy;

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

- write_lock_irqsave(&cpufreq_driver_lock, flags);
-
+ read_lock_irqsave(&cpufreq_driver_lock, flags);
policy = per_cpu(cpufreq_cpu_data, cpu);
-
- /* Save the policy somewhere when doing a light-weight tear-down */
- if (cpufreq_suspended)
- per_cpu(cpufreq_cpu_data_fallback, cpu) = policy;
-
- write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ read_unlock_irqrestore(&cpufreq_driver_lock, flags);

if (!policy) {
pr_debug("%s: No cpu_data found\n", __func__);
@@ -1369,24 +1354,15 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
}
}

- if (!cpufreq_driver->setpolicy)
- strncpy(per_cpu(cpufreq_cpu_governor, cpu),
- policy->governor->name, CPUFREQ_NAME_LEN);
-
down_read(&policy->rwsem);
cpus = cpumask_weight(policy->cpus);
up_read(&policy->rwsem);

- if (cpu != policy->cpu) {
- sysfs_remove_link(&dev->kobj, "cpufreq");
- } else if (cpus > 1) {
- new_cpu = cpufreq_nominate_new_policy_cpu(policy, cpu);
- if (new_cpu >= 0) {
- update_policy_cpu(policy, new_cpu);
-
- if (!cpufreq_suspended)
- pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n",
- __func__, new_cpu, cpu);
+ if (cpus > 1) {
+ if (cpu == policy->cpu) {
+ new_cpu = cpumask_any_but(policy->cpus, cpu);
+ if (new_cpu >= 0)
+ update_policy_cpu(policy, new_cpu);
}
} else if (cpufreq_driver->stop_cpu && cpufreq_driver->setpolicy) {
cpufreq_driver->stop_cpu(policy);
@@ -1431,6 +1407,9 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
cpus = cpumask_weight(policy->cpus);
up_read(&policy->rwsem);

+ if (cpu != policy->kobj_cpu)
+ sysfs_remove_link(&dev->kobj, "cpufreq");
+
/* If cpu is last user of policy, free policy */
if (cpus == 0) {
if (has_target()) {
@@ -1475,12 +1454,10 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
static int cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
{
unsigned int cpu = dev->id;
- int ret;
-
- if (cpu_is_offline(cpu))
- return 0;
+ int ret = 0;

- ret = __cpufreq_remove_dev_prepare(dev, sif);
+ if (cpu_online(cpu))
+ ret = __cpufreq_remove_dev_prepare(dev, sif);

if (!ret)
ret = __cpufreq_remove_dev_finish(dev, sif);
@@ -2307,10 +2284,6 @@ static int cpufreq_cpu_callback(struct notifier_block *nfb,
__cpufreq_remove_dev_prepare(dev, NULL);
break;

- case CPU_POST_DEAD:
- __cpufreq_remove_dev_finish(dev, NULL);
- break;
-
case CPU_DOWN_FAILED:
__cpufreq_add_dev(dev, NULL);
break;
--
1.8.2.1
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