On 08/07/2014 03:48 AM, Viresh Kumar wrote:

On 25 July 2014 06:37, Saravana Kannan [off-list ref] wrote:

quoted

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 <redacted>
---
  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()) {

Probably cpumask_empty() would be more readable here.

Agreed.

quoted

                 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 */

I think I have already asked you to use proper comment style?

I did. Then I think I noticed some of the existing comments did keep the 
/* in its own line even for multiline comments. So, I got confused. Will 
fix.

quoted

+       recover_policy = false;

For this patch, probably it will work fine but I hope you will get rid of
this variable completely in next patches..

Yup. In 5/5

quoted

@@ -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;

Why?

Apparently for no good reason :) Probably some stale change when I was 
splitting up the patches. I'll double check and remove this.

quoted

         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);
-

Why? Probably I did mention this earlier as well?

This code is saving the governor name here to restore it when the policy 
is created again after suspend/resume or hotplug of all CPUs. Since we 
no longer throw away the policy struct, there's no point in doing this.

I should remove this per cpu variable though. Will do it in v5.

quoted

         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)

Can this ever be false?

If this is the last CPU going down. This part of the code didn't really 
change. I just moved the cpumask_any_but() from nominate policy to here 
since I'm not longer moving the kobj around.

quoted

+                               update_policy_cpu(policy, new_cpu);
                 }
         } else if (cpufreq_driver->stop_cpu && cpufreq_driver->setpolicy) {
                 cpufreq_driver->stop_cpu(policy);

quoted

@@ -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");
+

Why?

For the physical hot-remove case or when the cpufreq driver is unregistered.

quoted

         /* 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);

Why do you need a change here?

Since we no longer do remove_dev_finish during hotplug, we can't just 
short circuit the entire function. We have to finish the remove when the 
CPU is hot-removed or when the cpufreq driver is unregistered.

quoted

         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;
-

Sure? Who will call dev_finish() now?

At this point, all remove_dev_finish() does is remove the sysfs links 
and destroy the policy. So, it never needs to be called for hotplug. 
Only during physical hot-remove or during cpufreq driver unregister.

quoted

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

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-Saravana

-- 
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hosted by The Linux Foundation