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Date:	Thu, 7 Aug 2014 16:18:37 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	Todd Poynor <toddpoynor@...gle.com>,
	"Srivatsa S . Bhat" <srivatsa@....edu>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v4 3/5] cpufreq: Don't destroy/realloc policy/sysfs on hotplug/suspend

On 25 July 2014 06:37, Saravana Kannan <skannan@...eaurora.org> wrote:
> 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@...eaurora.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()) {

Probably cpumask_empty() would be more readable here.

>                 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?

> +       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..


> @@ -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?

>         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?

>         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?

> +                               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");
> +

Why?

>         /* 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?

>         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?

>                 case CPU_DOWN_FAILED:
>                         __cpufreq_add_dev(dev, NULL);
>                         break;
> --
> 1.8.2.1
>
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> hosted by The Linux Foundation
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