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Message-ID: <3141717.0s1tLjazMZ@vostro.rjw.lan>
Date: Thu, 31 Jul 2014 23:56:36 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Saravana Kannan <skannan@...eaurora.org>
Cc: Viresh Kumar <viresh.kumar@...aro.org>,
Todd Poynor <toddpoynor@...gle.com>,
"Srivatsa S . Bhat" <srivatsa@....edu>, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.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 Thursday, July 24, 2014 06:07:26 PM Saravana Kannan 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.
I'm still quite unsure how this is going to work with the real CPU hot-remove
that makes the entire sysfs cpu directories go away. Can you please explain
that?
> 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()) {
> 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;
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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