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Subject[PATCH 4/5] cpufreq: Simplify __cpufreq_remove_dev()
Date
__cpufreq_remove_dev() is called on multiple occasions: cpufreq_driver
unregister and cpu removals.

Current implementation of this routine is overly complex without much need. If
the cpu to be removed is the policy->cpu, we remove the policy first and add all
other cpus again from policy->cpus and then finally call __cpufreq_remove_dev()
again to remove the cpu to be deleted. Haahhhh..

There exist a simple solution to removal of a cpu:
- Simply use the old policy structure
- update its fields like: policy->cpu, etc.
- notify any users of cpufreq, which depend on changing policy->cpu

Hence this patch, which tries to implement the above theory. It is tested well
by myself on ARM big.LITTLE TC2 SoC, which has 5 cores (2 A15 and 3 A7). Both
A15's share same struct policy and all A7's share same policy structure.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
---
drivers/cpufreq/cpufreq.c | 159 +++++++++++++++++-----------------------
drivers/cpufreq/cpufreq_stats.c | 27 ++++++-
drivers/cpufreq/freq_table.c | 9 +++
include/linux/cpufreq.h | 14 ++--
4 files changed, 111 insertions(+), 98 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 034d183..f1bab33 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1036,6 +1036,23 @@ module_out:
return ret;
}

+static void update_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu)
+{
+ int j;
+
+ policy->last_cpu = policy->cpu;
+ policy->cpu = cpu;
+
+ for_each_cpu(j, policy->cpus) {
+ if (!cpu_online(j))
+ continue;
+ per_cpu(cpufreq_policy_cpu, j) = cpu;
+ }
+
+ cpufreq_frequency_table_update_policy_cpu(policy);
+ blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
+ CPUFREQ_UPDATE_POLICY_CPU, policy);
+}

/**
* __cpufreq_remove_dev - remove a CPU device
@@ -1046,132 +1063,92 @@ module_out:
*/
static int __cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
{
- unsigned int cpu = dev->id;
+ unsigned int cpu = dev->id, ret, cpus;
unsigned long flags;
struct cpufreq_policy *data;
struct kobject *kobj;
struct completion *cmp;
-#ifdef CONFIG_SMP
struct device *cpu_dev;
- unsigned int j;
-#endif

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

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

if (!data) {
+ pr_debug("%s: No cpu_data found\n", __func__);
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
unlock_policy_rwsem_write(cpu);
return -EINVAL;
}
- per_cpu(cpufreq_cpu_data, cpu) = NULL;

-#ifdef CONFIG_SMP
- /* if this isn't the CPU which is the parent of the kobj, we
- * only need to unlink, put and exit
- */
- if (unlikely(cpu != data->cpu)) {
- pr_debug("removing link\n");
+ if (cpufreq_driver->target)
__cpufreq_governor(data, CPUFREQ_GOV_STOP);
- cpumask_clear_cpu(cpu, data->cpus);
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
-
- __cpufreq_governor(data, CPUFREQ_GOV_START);
- __cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
-
- kobj = &dev->kobj;
- cpufreq_cpu_put(data);
- unlock_policy_rwsem_write(cpu);
- sysfs_remove_link(kobj, "cpufreq");
- return 0;
- }
-#endif
-
-#ifdef CONFIG_SMP

#ifdef CONFIG_HOTPLUG_CPU
strncpy(per_cpu(cpufreq_cpu_governor, cpu), data->governor->name,
CPUFREQ_NAME_LEN);
#endif

- /* if we have other CPUs still registered, we need to unlink them,
- * or else wait_for_completion below will lock up. Clean the
- * per_cpu(cpufreq_cpu_data) while holding the lock, and remove
- * the sysfs links afterwards.
- */
- if (unlikely(cpumask_weight(data->cpus) > 1)) {
- for_each_cpu(j, data->cpus) {
- if (j == cpu)
- continue;
- per_cpu(cpufreq_cpu_data, j) = NULL;
- }
- }
-
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
+ per_cpu(cpufreq_cpu_data, cpu) = NULL;
+ cpus = cpumask_weight(data->cpus);
+ cpumask_clear_cpu(cpu, data->cpus);

- if (unlikely(cpumask_weight(data->cpus) > 1)) {
- for_each_cpu(j, data->cpus) {
- if (j == cpu)
- continue;
- pr_debug("removing link for cpu %u\n", j);
-#ifdef CONFIG_HOTPLUG_CPU
- strncpy(per_cpu(cpufreq_cpu_governor, j),
- data->governor->name, CPUFREQ_NAME_LEN);
-#endif
- cpu_dev = get_cpu_device(j);
- kobj = &cpu_dev->kobj;
+ if (unlikely((cpu == data->cpu) && (cpus > 1))) {
+ /* first sibling now owns the new sysfs dir */
+ cpu_dev = get_cpu_device(cpumask_first(data->cpus));
+ sysfs_remove_link(&cpu_dev->kobj, "cpufreq");
+ ret = kobject_move(&data->kobj, &cpu_dev->kobj);
+ if (ret) {
+ pr_err("%s: Failed to move kobj: %d", __func__, ret);
+ cpumask_set_cpu(cpu, data->cpus);
+ ret = sysfs_create_link(&cpu_dev->kobj, &data->kobj,
+ "cpufreq");
+ spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
unlock_policy_rwsem_write(cpu);
- sysfs_remove_link(kobj, "cpufreq");
- lock_policy_rwsem_write(cpu);
- cpufreq_cpu_put(data);
+ return -EINVAL;
}
+
+ update_policy_cpu(data, cpu_dev->id);
+ pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n",
+ __func__, cpu_dev->id, cpu);
}
-#else
- spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
-#endif

- if (cpufreq_driver->target)
- __cpufreq_governor(data, CPUFREQ_GOV_STOP);
+ spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

- kobj = &data->kobj;
- cmp = &data->kobj_unregister;
+ pr_debug("%s: removing link, cpu: %d\n", __func__, cpu);
+ cpufreq_cpu_put(data);
unlock_policy_rwsem_write(cpu);
- kobject_put(kobj);
+ sysfs_remove_link(&dev->kobj, "cpufreq");

- /* we need to make sure that the underlying kobj is actually
- * not referenced anymore by anybody before we proceed with
- * unloading.
- */
- pr_debug("waiting for dropping of refcount\n");
- wait_for_completion(cmp);
- pr_debug("wait complete\n");
-
- lock_policy_rwsem_write(cpu);
- if (cpufreq_driver->exit)
- cpufreq_driver->exit(data);
- unlock_policy_rwsem_write(cpu);
+ /* If cpu is last user of policy, free policy */
+ if (cpus == 1) {
+ lock_policy_rwsem_write(cpu);
+ kobj = &data->kobj;
+ cmp = &data->kobj_unregister;
+ unlock_policy_rwsem_write(cpu);
+ kobject_put(kobj);

-#ifdef CONFIG_HOTPLUG_CPU
- /* when the CPU which is the parent of the kobj is hotplugged
- * offline, check for siblings, and create cpufreq sysfs interface
- * and symlinks
- */
- if (unlikely(cpumask_weight(data->cpus) > 1)) {
- /* first sibling now owns the new sysfs dir */
- cpumask_clear_cpu(cpu, data->cpus);
- cpufreq_add_dev(get_cpu_device(cpumask_first(data->cpus)), NULL);
+ /* we need to make sure that the underlying kobj is actually
+ * not referenced anymore by anybody before we proceed with
+ * unloading.
+ */
+ pr_debug("waiting for dropping of refcount\n");
+ wait_for_completion(cmp);
+ pr_debug("wait complete\n");

- /* finally remove our own symlink */
lock_policy_rwsem_write(cpu);
- __cpufreq_remove_dev(dev, sif);
- }
-#endif
+ if (cpufreq_driver->exit)
+ cpufreq_driver->exit(data);
+ unlock_policy_rwsem_write(cpu);

- free_cpumask_var(data->related_cpus);
- free_cpumask_var(data->cpus);
- kfree(data);
+ free_cpumask_var(data->related_cpus);
+ free_cpumask_var(data->cpus);
+ kfree(data);
+ } else if (cpufreq_driver->target) {
+ __cpufreq_governor(data, CPUFREQ_GOV_START);
+ __cpufreq_governor(data, CPUFREQ_GOV_LIMITS);
+ }

return 0;
}
diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index e40e508..251719a 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -170,11 +170,13 @@ static int freq_table_get_index(struct cpufreq_stats *stat, unsigned int freq)
static void cpufreq_stats_free_table(unsigned int cpu)
{
struct cpufreq_stats *stat = per_cpu(cpufreq_stats_table, cpu);
+
if (stat) {
+ pr_debug("%s: Free stat table\n", __func__);
kfree(stat->time_in_state);
kfree(stat);
+ per_cpu(cpufreq_stats_table, cpu) = NULL;
}
- per_cpu(cpufreq_stats_table, cpu) = NULL;
}

/* must be called early in the CPU removal sequence (before
@@ -183,8 +185,10 @@ static void cpufreq_stats_free_table(unsigned int cpu)
static void cpufreq_stats_free_sysfs(unsigned int cpu)
{
struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
- if (policy && policy->cpu == cpu)
+ if (policy && (cpumask_weight(policy->cpus) == 1)) {
+ pr_debug("%s: Free sysfs stat\n", __func__);
sysfs_remove_group(&policy->kobj, &stats_attr_group);
+ }
if (policy)
cpufreq_cpu_put(policy);
}
@@ -262,6 +266,19 @@ error_get_fail:
return ret;
}

+static void cpufreq_stats_update_policy_cpu(struct cpufreq_policy *policy)
+{
+ struct cpufreq_stats *stat = per_cpu(cpufreq_stats_table,
+ policy->last_cpu);
+
+ pr_debug("Updating stats_table for new_cpu %u from last_cpu %u\n",
+ policy->cpu, policy->last_cpu);
+ per_cpu(cpufreq_stats_table, policy->cpu) = per_cpu(cpufreq_stats_table,
+ policy->last_cpu);
+ per_cpu(cpufreq_stats_table, policy->last_cpu) = NULL;
+ stat->cpu = policy->cpu;
+}
+
static int cpufreq_stat_notifier_policy(struct notifier_block *nb,
unsigned long val, void *data)
{
@@ -269,6 +286,12 @@ static int cpufreq_stat_notifier_policy(struct notifier_block *nb,
struct cpufreq_policy *policy = data;
struct cpufreq_frequency_table *table;
unsigned int cpu = policy->cpu;
+
+ if (val == CPUFREQ_UPDATE_POLICY_CPU) {
+ cpufreq_stats_update_policy_cpu(policy);
+ return 0;
+ }
+
if (val != CPUFREQ_NOTIFY)
return 0;
table = cpufreq_frequency_get_table(cpu);
diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
index 49cda25..aa5bd39 100644
--- a/drivers/cpufreq/freq_table.c
+++ b/drivers/cpufreq/freq_table.c
@@ -227,6 +227,15 @@ void cpufreq_frequency_table_put_attr(unsigned int cpu)
}
EXPORT_SYMBOL_GPL(cpufreq_frequency_table_put_attr);

+void cpufreq_frequency_table_update_policy_cpu(struct cpufreq_policy *policy)
+{
+ pr_debug("Updating show_table for new_cpu %u from last_cpu %u\n",
+ policy->cpu, policy->last_cpu);
+ per_cpu(cpufreq_show_table, policy->cpu) = per_cpu(cpufreq_show_table,
+ policy->last_cpu);
+ per_cpu(cpufreq_show_table, policy->last_cpu) = NULL;
+}
+
struct cpufreq_frequency_table *cpufreq_frequency_get_table(unsigned int cpu)
{
return per_cpu(cpufreq_show_table, cpu);
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index a55b88e..52be2d0 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -93,7 +93,9 @@ struct cpufreq_policy {
cpumask_var_t related_cpus; /* CPUs with any coordination */
unsigned int shared_type; /* ANY or ALL affected CPUs
should set cpufreq */
- unsigned int cpu; /* cpu nr of registered CPU */
+ unsigned int cpu; /* cpu nr of CPU managing this policy */
+ unsigned int last_cpu; /* cpu nr of previous CPU that managed
+ * this policy */
struct cpufreq_cpuinfo cpuinfo;/* see above */

unsigned int min; /* in kHz */
@@ -112,10 +114,11 @@ struct cpufreq_policy {
struct completion kobj_unregister;
};

-#define CPUFREQ_ADJUST (0)
-#define CPUFREQ_INCOMPATIBLE (1)
-#define CPUFREQ_NOTIFY (2)
-#define CPUFREQ_START (3)
+#define CPUFREQ_ADJUST (0)
+#define CPUFREQ_INCOMPATIBLE (1)
+#define CPUFREQ_NOTIFY (2)
+#define CPUFREQ_START (3)
+#define CPUFREQ_UPDATE_POLICY_CPU (4)

#define CPUFREQ_SHARED_TYPE_NONE (0) /* None */
#define CPUFREQ_SHARED_TYPE_HW (1) /* HW does needed coordination */
@@ -405,6 +408,7 @@ extern struct freq_attr cpufreq_freq_attr_scaling_available_freqs;

void cpufreq_frequency_table_get_attr(struct cpufreq_frequency_table *table,
unsigned int cpu);
+void cpufreq_frequency_table_update_policy_cpu(struct cpufreq_policy *policy);

void cpufreq_frequency_table_put_attr(unsigned int cpu);
#endif /* _LINUX_CPUFREQ_H */
--
1.7.12.rc2.18.g61b472e


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