From b7898fda5bc7e786e76ce24fbd2ec993b08ec518 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Wed, 30 Mar 2016 03:47:49 +0200 Subject: [PATCH] cpufreq: Support for fast frequency switching Modify the ACPI cpufreq driver to provide a method for switching CPU frequencies from interrupt context and update the cpufreq core to support that method if available. Introduce a new cpufreq driver callback, ->fast_switch, to be invoked for frequency switching from interrupt context by (future) governors supporting that feature via (new) helper function cpufreq_driver_fast_switch(). Add two new policy flags, fast_switch_possible, to be set by the cpufreq driver if fast frequency switching can be used for the given policy and fast_switch_enabled, to be set by the governor if it is going to use fast frequency switching for the given policy. Also add a helper for setting the latter. Since fast frequency switching is inherently incompatible with cpufreq transition notifiers, make it possible to set the fast_switch_enabled only if there are no transition notifiers already registered and make the registration of new transition notifiers fail if fast_switch_enabled is set for at least one policy. Implement the ->fast_switch callback in the ACPI cpufreq driver and make it set fast_switch_possible during policy initialization as appropriate. Signed-off-by: Rafael J. Wysocki Acked-by: Viresh Kumar --- drivers/cpufreq/acpi-cpufreq.c | 42 +++++++++++ drivers/cpufreq/cpufreq.c | 130 +++++++++++++++++++++++++++++++-- include/linux/cpufreq.h | 16 ++++ 3 files changed, 183 insertions(+), 5 deletions(-) diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c index fb5712141040..7f38fb55f223 100644 --- a/drivers/cpufreq/acpi-cpufreq.c +++ b/drivers/cpufreq/acpi-cpufreq.c @@ -458,6 +458,43 @@ static int acpi_cpufreq_target(struct cpufreq_policy *policy, return result; } +unsigned int acpi_cpufreq_fast_switch(struct cpufreq_policy *policy, + unsigned int target_freq) +{ + struct acpi_cpufreq_data *data = policy->driver_data; + struct acpi_processor_performance *perf; + struct cpufreq_frequency_table *entry; + unsigned int next_perf_state, next_freq, freq; + + /* + * Find the closest frequency above target_freq. + * + * The table is sorted in the reverse order with respect to the + * frequency and all of the entries are valid (see the initialization). + */ + entry = data->freq_table; + do { + entry++; + freq = entry->frequency; + } while (freq >= target_freq && freq != CPUFREQ_TABLE_END); + entry--; + next_freq = entry->frequency; + next_perf_state = entry->driver_data; + + perf = to_perf_data(data); + if (perf->state == next_perf_state) { + if (unlikely(data->resume)) + data->resume = 0; + else + return next_freq; + } + + data->cpu_freq_write(&perf->control_register, + perf->states[next_perf_state].control); + perf->state = next_perf_state; + return next_freq; +} + static unsigned long acpi_cpufreq_guess_freq(struct acpi_cpufreq_data *data, unsigned int cpu) { @@ -821,6 +858,9 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy) */ data->resume = 1; + policy->fast_switch_possible = !acpi_pstate_strict && + !(policy_is_shared(policy) && policy->shared_type != CPUFREQ_SHARED_TYPE_ANY); + return result; err_freqfree: @@ -843,6 +883,7 @@ static int acpi_cpufreq_cpu_exit(struct cpufreq_policy *policy) pr_debug("acpi_cpufreq_cpu_exit\n"); if (data) { + policy->fast_switch_possible = false; policy->driver_data = NULL; acpi_processor_unregister_performance(data->acpi_perf_cpu); free_cpumask_var(data->freqdomain_cpus); @@ -876,6 +917,7 @@ static struct freq_attr *acpi_cpufreq_attr[] = { static struct cpufreq_driver acpi_cpufreq_driver = { .verify = cpufreq_generic_frequency_table_verify, .target_index = acpi_cpufreq_target, + .fast_switch = acpi_cpufreq_fast_switch, .bios_limit = acpi_processor_get_bios_limit, .init = acpi_cpufreq_cpu_init, .exit = acpi_cpufreq_cpu_exit, diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index b87596b591b3..a5b7d77d4816 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -77,6 +77,7 @@ static inline bool has_target(void) static int cpufreq_governor(struct cpufreq_policy *policy, unsigned int event); static unsigned int __cpufreq_get(struct cpufreq_policy *policy); static int cpufreq_start_governor(struct cpufreq_policy *policy); +static int cpufreq_exit_governor(struct cpufreq_policy *policy); /** * Two notifier lists: the "policy" list is involved in the @@ -429,6 +430,68 @@ void cpufreq_freq_transition_end(struct cpufreq_policy *policy, } EXPORT_SYMBOL_GPL(cpufreq_freq_transition_end); +/* + * Fast frequency switching status count. Positive means "enabled", negative + * means "disabled" and 0 means "not decided yet". + */ +static int cpufreq_fast_switch_count; +static DEFINE_MUTEX(cpufreq_fast_switch_lock); + +static void cpufreq_list_transition_notifiers(void) +{ + struct notifier_block *nb; + + pr_info("Registered transition notifiers:\n"); + + mutex_lock(&cpufreq_transition_notifier_list.mutex); + + for (nb = cpufreq_transition_notifier_list.head; nb; nb = nb->next) + pr_info("%pF\n", nb->notifier_call); + + mutex_unlock(&cpufreq_transition_notifier_list.mutex); +} + +/** + * cpufreq_enable_fast_switch - Enable fast frequency switching for policy. + * @policy: cpufreq policy to enable fast frequency switching for. + * + * Try to enable fast frequency switching for @policy. + * + * The attempt will fail if there is at least one transition notifier registered + * at this point, as fast frequency switching is quite fundamentally at odds + * with transition notifiers. Thus if successful, it will make registration of + * transition notifiers fail going forward. + */ +void cpufreq_enable_fast_switch(struct cpufreq_policy *policy) +{ + lockdep_assert_held(&policy->rwsem); + + if (!policy->fast_switch_possible) + return; + + mutex_lock(&cpufreq_fast_switch_lock); + if (cpufreq_fast_switch_count >= 0) { + cpufreq_fast_switch_count++; + policy->fast_switch_enabled = true; + } else { + pr_warn("CPU%u: Fast frequency switching not enabled\n", + policy->cpu); + cpufreq_list_transition_notifiers(); + } + mutex_unlock(&cpufreq_fast_switch_lock); +} +EXPORT_SYMBOL_GPL(cpufreq_enable_fast_switch); + +static void cpufreq_disable_fast_switch(struct cpufreq_policy *policy) +{ + mutex_lock(&cpufreq_fast_switch_lock); + if (policy->fast_switch_enabled) { + policy->fast_switch_enabled = false; + if (!WARN_ON(cpufreq_fast_switch_count <= 0)) + cpufreq_fast_switch_count--; + } + mutex_unlock(&cpufreq_fast_switch_lock); +} /********************************************************************* * SYSFS INTERFACE * @@ -1319,7 +1382,7 @@ static void cpufreq_offline(unsigned int cpu) /* If cpu is last user of policy, free policy */ if (has_target()) { - ret = cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); + ret = cpufreq_exit_governor(policy); if (ret) pr_err("%s: Failed to exit governor\n", __func__); } @@ -1447,8 +1510,12 @@ static unsigned int __cpufreq_get(struct cpufreq_policy *policy) ret_freq = cpufreq_driver->get(policy->cpu); - /* Updating inactive policies is invalid, so avoid doing that. */ - if (unlikely(policy_is_inactive(policy))) + /* + * Updating inactive policies is invalid, so avoid doing that. Also + * if fast frequency switching is used with the given policy, the check + * against policy->cur is pointless, so skip it in that case too. + */ + if (unlikely(policy_is_inactive(policy)) || policy->fast_switch_enabled) return ret_freq; if (ret_freq && policy->cur && @@ -1672,8 +1739,18 @@ int cpufreq_register_notifier(struct notifier_block *nb, unsigned int list) switch (list) { case CPUFREQ_TRANSITION_NOTIFIER: + mutex_lock(&cpufreq_fast_switch_lock); + + if (cpufreq_fast_switch_count > 0) { + mutex_unlock(&cpufreq_fast_switch_lock); + return -EBUSY; + } ret = srcu_notifier_chain_register( &cpufreq_transition_notifier_list, nb); + if (!ret) + cpufreq_fast_switch_count--; + + mutex_unlock(&cpufreq_fast_switch_lock); break; case CPUFREQ_POLICY_NOTIFIER: ret = blocking_notifier_chain_register( @@ -1706,8 +1783,14 @@ int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list) switch (list) { case CPUFREQ_TRANSITION_NOTIFIER: + mutex_lock(&cpufreq_fast_switch_lock); + ret = srcu_notifier_chain_unregister( &cpufreq_transition_notifier_list, nb); + if (!ret && !WARN_ON(cpufreq_fast_switch_count >= 0)) + cpufreq_fast_switch_count++; + + mutex_unlock(&cpufreq_fast_switch_lock); break; case CPUFREQ_POLICY_NOTIFIER: ret = blocking_notifier_chain_unregister( @@ -1726,6 +1809,37 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier); * GOVERNORS * *********************************************************************/ +/** + * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch. + * @policy: cpufreq policy to switch the frequency for. + * @target_freq: New frequency to set (may be approximate). + * + * Carry out a fast frequency switch without sleeping. + * + * The driver's ->fast_switch() callback invoked by this function must be + * suitable for being called from within RCU-sched read-side critical sections + * and it is expected to select the minimum available frequency greater than or + * equal to @target_freq (CPUFREQ_RELATION_L). + * + * This function must not be called if policy->fast_switch_enabled is unset. + * + * Governors calling this function must guarantee that it will never be invoked + * twice in parallel for the same policy and that it will never be called in + * parallel with either ->target() or ->target_index() for the same policy. + * + * If CPUFREQ_ENTRY_INVALID is returned by the driver's ->fast_switch() + * callback to indicate an error condition, the hardware configuration must be + * preserved. + */ +unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, + unsigned int target_freq) +{ + clamp_val(target_freq, policy->min, policy->max); + + return cpufreq_driver->fast_switch(policy, target_freq); +} +EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch); + /* Must set freqs->new to intermediate frequency */ static int __target_intermediate(struct cpufreq_policy *policy, struct cpufreq_freqs *freqs, int index) @@ -1946,6 +2060,12 @@ static int cpufreq_start_governor(struct cpufreq_policy *policy) return ret ? ret : cpufreq_governor(policy, CPUFREQ_GOV_LIMITS); } +static int cpufreq_exit_governor(struct cpufreq_policy *policy) +{ + cpufreq_disable_fast_switch(policy); + return cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); +} + int cpufreq_register_governor(struct cpufreq_governor *governor) { int err; @@ -2101,7 +2221,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, return ret; } - ret = cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); + ret = cpufreq_exit_governor(policy); if (ret) { pr_err("%s: Failed to Exit Governor: %s (%d)\n", __func__, old_gov->name, ret); @@ -2118,7 +2238,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy, pr_debug("cpufreq: governor change\n"); return 0; } - cpufreq_governor(policy, CPUFREQ_GOV_POLICY_EXIT); + cpufreq_exit_governor(policy); } /* new governor failed, so re-start old one */ diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 2b4f248b8ef1..55e69ebb035c 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -102,6 +102,17 @@ struct cpufreq_policy { */ struct rw_semaphore rwsem; + /* + * Fast switch flags: + * - fast_switch_possible should be set by the driver if it can + * guarantee that frequency can be changed on any CPU sharing the + * policy and that the change will affect all of the policy CPUs then. + * - fast_switch_enabled is to be set by governors that support fast + * freqnency switching with the help of cpufreq_enable_fast_switch(). + */ + bool fast_switch_possible; + bool fast_switch_enabled; + /* Synchronization for frequency transitions */ bool transition_ongoing; /* Tracks transition status */ spinlock_t transition_lock; @@ -156,6 +167,7 @@ int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu); int cpufreq_update_policy(unsigned int cpu); bool have_governor_per_policy(void); struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy); +void cpufreq_enable_fast_switch(struct cpufreq_policy *policy); #else static inline unsigned int cpufreq_get(unsigned int cpu) { @@ -236,6 +248,8 @@ struct cpufreq_driver { unsigned int relation); /* Deprecated */ int (*target_index)(struct cpufreq_policy *policy, unsigned int index); + unsigned int (*fast_switch)(struct cpufreq_policy *policy, + unsigned int target_freq); /* * Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION * unset. @@ -464,6 +478,8 @@ struct cpufreq_governor { }; /* Pass a target to the cpufreq driver */ +unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, + unsigned int target_freq); int cpufreq_driver_target(struct cpufreq_policy *policy, unsigned int target_freq, unsigned int relation); -- 2.20.1