On 10/02/2013 02:13 PM, Viresh Kumar wrote: > We have per-cpu cpu_policy_rwsem for cpufreq core, but we never use all of > them. > We always use rwsem of policy->cpu and so we can actually make this rwsem per > policy instead. > > This patch does this change. With this change other tricky situations are also > avoided now, like which lock to take while we are changing policy->cpu, etc. > > Suggested-by: Srivatsa S. Bhat <[email protected]> > Signed-off-by: Viresh Kumar <[email protected]> > ---
This is a very nice improvement! Reviewed-by: Srivatsa S. Bhat <[email protected]> Regards, Srivatsa S. Bhat > drivers/cpufreq/cpufreq.c | 110 > +++++++++++++--------------------------------- > include/linux/cpufreq.h | 14 ++++++ > 2 files changed, 45 insertions(+), 79 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index eb993d9..ae866b1 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -48,47 +48,6 @@ static DEFINE_PER_CPU(char[CPUFREQ_NAME_LEN], > cpufreq_cpu_governor); > #endif > > /* > - * cpu_policy_rwsem is a per CPU reader-writer semaphore designed to cure > - * all cpufreq/hotplug/workqueue/etc related lock issues. > - * > - * The rules for this semaphore: > - * - Any routine that wants to read from the policy structure will > - * do a down_read on this semaphore. > - * - Any routine that will write to the policy structure and/or may take away > - * the policy altogether (eg. CPU hotplug), will hold this lock in write > - * mode before doing so. > - * > - * Additional rules: > - * - Governor routines that can be called in cpufreq hotplug path should not > - * take this sem as top level hotplug notifier handler takes this. > - * - Lock should not be held across > - * __cpufreq_governor(data, CPUFREQ_GOV_STOP); > - */ > -static DEFINE_PER_CPU(struct rw_semaphore, cpu_policy_rwsem); > - > -#define lock_policy_rwsem(mode, cpu) \ > -static void lock_policy_rwsem_##mode(int cpu) > \ > -{ \ > - struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu); \ > - BUG_ON(!policy); \ > - down_##mode(&per_cpu(cpu_policy_rwsem, policy->cpu)); \ > -} > - > -lock_policy_rwsem(read, cpu); > -lock_policy_rwsem(write, cpu); > - > -#define unlock_policy_rwsem(mode, cpu) > \ > -static void unlock_policy_rwsem_##mode(int cpu) > \ > -{ \ > - struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu); \ > - BUG_ON(!policy); \ > - up_##mode(&per_cpu(cpu_policy_rwsem, policy->cpu)); \ > -} > - > -unlock_policy_rwsem(read, cpu); > -unlock_policy_rwsem(write, cpu); > - > -/* > * rwsem to guarantee that cpufreq driver module doesn't unload during > critical > * sections > */ > @@ -656,14 +615,14 @@ static ssize_t show(struct kobject *kobj, struct > attribute *attr, char *buf) > if (!down_read_trylock(&cpufreq_rwsem)) > return -EINVAL; > > - lock_policy_rwsem_read(policy->cpu); > + down_read(&policy->rwsem); > > if (fattr->show) > ret = fattr->show(policy, buf); > else > ret = -EIO; > > - unlock_policy_rwsem_read(policy->cpu); > + up_read(&policy->rwsem); > up_read(&cpufreq_rwsem); > > return ret; > @@ -684,14 +643,14 @@ static ssize_t store(struct kobject *kobj, struct > attribute *attr, > if (!down_read_trylock(&cpufreq_rwsem)) > goto unlock; > > - lock_policy_rwsem_write(policy->cpu); > + down_write(&policy->rwsem); > > if (fattr->store) > ret = fattr->store(policy, buf, count); > else > ret = -EIO; > > - unlock_policy_rwsem_write(policy->cpu); > + up_write(&policy->rwsem); > > up_read(&cpufreq_rwsem); > unlock: > @@ -868,7 +827,7 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy > *policy, > } > } > > - lock_policy_rwsem_write(policy->cpu); > + down_write(&policy->rwsem); > > write_lock_irqsave(&cpufreq_driver_lock, flags); > > @@ -876,7 +835,7 @@ static int cpufreq_add_policy_cpu(struct cpufreq_policy > *policy, > per_cpu(cpufreq_cpu_data, cpu) = policy; > write_unlock_irqrestore(&cpufreq_driver_lock, flags); > > - unlock_policy_rwsem_write(policy->cpu); > + up_write(&policy->rwsem); > > if (has_target) { > if ((ret = __cpufreq_governor(policy, CPUFREQ_GOV_START)) || > @@ -923,6 +882,8 @@ static struct cpufreq_policy *cpufreq_policy_alloc(void) > goto err_free_cpumask; > > INIT_LIST_HEAD(&policy->policy_list); > + init_rwsem(&policy->rwsem); > + > return policy; > > err_free_cpumask: > @@ -945,19 +906,12 @@ static void update_policy_cpu(struct cpufreq_policy > *policy, unsigned int cpu) > if (cpu == policy->cpu) > return; > > - /* > - * Take direct locks as lock_policy_rwsem_write wouldn't work here. > - * Also lock for last cpu is enough here as contention will happen only > - * after policy->cpu is changed and after it is changed, other threads > - * will try to acquire lock for new cpu. And policy is already updated > - * by then. > - */ > - down_write(&per_cpu(cpu_policy_rwsem, policy->cpu)); > + down_write(&policy->rwsem); > > policy->last_cpu = policy->cpu; > policy->cpu = cpu; > > - up_write(&per_cpu(cpu_policy_rwsem, policy->last_cpu)); > + up_write(&policy->rwsem); > > #ifdef CONFIG_CPU_FREQ_TABLE > cpufreq_frequency_table_update_policy_cpu(policy); > @@ -1140,9 +1094,9 @@ static int cpufreq_nominate_new_policy_cpu(struct > cpufreq_policy *policy, > if (ret) { > pr_err("%s: Failed to move kobj: %d", __func__, ret); > > - lock_policy_rwsem_write(old_cpu); > + down_write(&policy->rwsem); > cpumask_set_cpu(old_cpu, policy->cpus); > - unlock_policy_rwsem_write(old_cpu); > + up_write(&policy->rwsem); > > ret = sysfs_create_link(&cpu_dev->kobj, &policy->kobj, > "cpufreq"); > @@ -1193,9 +1147,9 @@ static int __cpufreq_remove_dev_prepare(struct device > *dev, > policy->governor->name, CPUFREQ_NAME_LEN); > #endif > > - lock_policy_rwsem_read(cpu); > + down_read(&policy->rwsem); > cpus = cpumask_weight(policy->cpus); > - unlock_policy_rwsem_read(cpu); > + up_read(&policy->rwsem); > > if (cpu != policy->cpu) { > if (!frozen) > @@ -1236,12 +1190,12 @@ static int __cpufreq_remove_dev_finish(struct device > *dev, > return -EINVAL; > } > > - lock_policy_rwsem_write(cpu); > + down_write(&policy->rwsem); > cpus = cpumask_weight(policy->cpus); > > if (cpus > 1) > cpumask_clear_cpu(cpu, policy->cpus); > - unlock_policy_rwsem_write(cpu); > + up_write(&policy->rwsem); > > /* If cpu is last user of policy, free policy */ > if (cpus == 1) { > @@ -1256,10 +1210,10 @@ static int __cpufreq_remove_dev_finish(struct device > *dev, > } > > if (!frozen) { > - lock_policy_rwsem_read(cpu); > + down_read(&policy->rwsem); > kobj = &policy->kobj; > cmp = &policy->kobj_unregister; > - unlock_policy_rwsem_read(cpu); > + up_read(&policy->rwsem); > kobject_put(kobj); > > /* > @@ -1451,19 +1405,22 @@ static unsigned int __cpufreq_get(unsigned int cpu) > */ > unsigned int cpufreq_get(unsigned int cpu) > { > + struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu); > unsigned int ret_freq = 0; > > if (cpufreq_disabled() || !cpufreq_driver) > return -ENOENT; > > + BUG_ON(!policy); > + > if (!down_read_trylock(&cpufreq_rwsem)) > return 0; > > - lock_policy_rwsem_read(cpu); > + down_read(&policy->rwsem); > > ret_freq = __cpufreq_get(cpu); > > - unlock_policy_rwsem_read(cpu); > + up_read(&policy->rwsem); > up_read(&cpufreq_rwsem); > > return ret_freq; > @@ -1687,11 +1644,11 @@ int cpufreq_driver_target(struct cpufreq_policy > *policy, > { > int ret = -EINVAL; > > - lock_policy_rwsem_write(policy->cpu); > + down_write(&policy->rwsem); > > ret = __cpufreq_driver_target(policy, target_freq, relation); > > - unlock_policy_rwsem_write(policy->cpu); > + up_write(&policy->rwsem); > > return ret; > } > @@ -1922,10 +1879,10 @@ static int __cpufreq_set_policy(struct cpufreq_policy > *policy, > /* end old governor */ > if (policy->governor) { > __cpufreq_governor(policy, CPUFREQ_GOV_STOP); > - unlock_policy_rwsem_write(new_policy->cpu); > + up_write(&new_policy->rwsem); > __cpufreq_governor(policy, > CPUFREQ_GOV_POLICY_EXIT); > - lock_policy_rwsem_write(new_policy->cpu); > + down_write(&new_policy->rwsem); > } > > /* start new governor */ > @@ -1934,10 +1891,10 @@ static int __cpufreq_set_policy(struct cpufreq_policy > *policy, > if (!__cpufreq_governor(policy, > CPUFREQ_GOV_START)) { > failed = 0; > } else { > - > unlock_policy_rwsem_write(new_policy->cpu); > + up_write(&new_policy->rwsem); > __cpufreq_governor(policy, > > CPUFREQ_GOV_POLICY_EXIT); > - > lock_policy_rwsem_write(new_policy->cpu); > + down_write(&new_policy->rwsem); > } > } > > @@ -1983,7 +1940,7 @@ int cpufreq_update_policy(unsigned int cpu) > goto no_policy; > } > > - lock_policy_rwsem_write(cpu); > + down_write(&policy->rwsem); > > pr_debug("updating policy for CPU %u\n", cpu); > memcpy(&new_policy, policy, sizeof(*policy)); > @@ -2010,7 +1967,7 @@ int cpufreq_update_policy(unsigned int cpu) > > ret = __cpufreq_set_policy(policy, &new_policy); > > - unlock_policy_rwsem_write(cpu); > + up_write(&policy->rwsem); > > cpufreq_cpu_put(policy); > no_policy: > @@ -2167,14 +2124,9 @@ EXPORT_SYMBOL_GPL(cpufreq_unregister_driver); > > static int __init cpufreq_core_init(void) > { > - int cpu; > - > if (cpufreq_disabled()) > return -ENODEV; > > - for_each_possible_cpu(cpu) > - init_rwsem(&per_cpu(cpu_policy_rwsem, cpu)); > - > cpufreq_global_kobject = kobject_create(); > BUG_ON(!cpufreq_global_kobject); > register_syscore_ops(&cpufreq_syscore_ops); > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h > index 6b199ed..a72bac2 100644 > --- a/include/linux/cpufreq.h > +++ b/include/linux/cpufreq.h > @@ -85,6 +85,20 @@ struct cpufreq_policy { > struct list_head policy_list; > struct kobject kobj; > struct completion kobj_unregister; > + > + /* > + * The rules for this semaphore: > + * - Any routine that wants to read from the policy structure will > + * do a down_read on this semaphore. > + * - Any routine that will write to the policy structure and/or may > take away > + * the policy altogether (eg. CPU hotplug), will hold this lock in > write > + * mode before doing so. > + * > + * Additional rules: > + * - Lock should not be held across > + * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT); > + */ > + struct rw_semaphore rwsem; > }; > > /* Only for ACPI */ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
