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cpufreq: Support for fast frequency switching
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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 <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
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rafaeljw committed Apr 1, 2016
1 parent 379480d commit b7898fd
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Showing 3 changed files with 183 additions and 5 deletions.
42 changes: 42 additions & 0 deletions drivers/cpufreq/acpi-cpufreq.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
{
Expand Down Expand Up @@ -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:
Expand All @@ -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);
Expand Down Expand Up @@ -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,
Expand Down
130 changes: 125 additions & 5 deletions drivers/cpufreq/cpufreq.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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 *
Expand Down Expand Up @@ -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__);
}
Expand Down Expand Up @@ -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 &&
Expand Down Expand Up @@ -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(
Expand Down Expand Up @@ -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(
Expand All @@ -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)
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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 */
Expand Down
16 changes: 16 additions & 0 deletions include/linux/cpufreq.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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)
{
Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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);
Expand Down

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