linux/drivers/cpufreq/cpufreq_governor.c
Paul E. McKenney cc69b389fd cpufreq/cpufreq_governor: Replace synchronize_sched() with synchronize_rcu()
Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu().  This commit therefore makes this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-27 09:21:38 -08:00

575 lines
16 KiB
C

/*
* drivers/cpufreq/cpufreq_governor.c
*
* CPUFREQ governors common code
*
* Copyright (C) 2001 Russell King
* (C) 2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
* (C) 2003 Jun Nakajima <jun.nakajima@intel.com>
* (C) 2009 Alexander Clouter <alex@digriz.org.uk>
* (c) 2012 Viresh Kumar <viresh.kumar@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/export.h>
#include <linux/kernel_stat.h>
#include <linux/slab.h>
#include "cpufreq_governor.h"
#define CPUFREQ_DBS_MIN_SAMPLING_INTERVAL (2 * TICK_NSEC / NSEC_PER_USEC)
static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs);
static DEFINE_MUTEX(gov_dbs_data_mutex);
/* Common sysfs tunables */
/**
* store_sampling_rate - update sampling rate effective immediately if needed.
*
* If new rate is smaller than the old, simply updating
* dbs.sampling_rate might not be appropriate. For example, if the
* original sampling_rate was 1 second and the requested new sampling rate is 10
* ms because the user needs immediate reaction from ondemand governor, but not
* sure if higher frequency will be required or not, then, the governor may
* change the sampling rate too late; up to 1 second later. Thus, if we are
* reducing the sampling rate, we need to make the new value effective
* immediately.
*
* This must be called with dbs_data->mutex held, otherwise traversing
* policy_dbs_list isn't safe.
*/
ssize_t store_sampling_rate(struct gov_attr_set *attr_set, const char *buf,
size_t count)
{
struct dbs_data *dbs_data = to_dbs_data(attr_set);
struct policy_dbs_info *policy_dbs;
unsigned int sampling_interval;
int ret;
ret = sscanf(buf, "%u", &sampling_interval);
if (ret != 1 || sampling_interval < CPUFREQ_DBS_MIN_SAMPLING_INTERVAL)
return -EINVAL;
dbs_data->sampling_rate = sampling_interval;
/*
* We are operating under dbs_data->mutex and so the list and its
* entries can't be freed concurrently.
*/
list_for_each_entry(policy_dbs, &attr_set->policy_list, list) {
mutex_lock(&policy_dbs->update_mutex);
/*
* On 32-bit architectures this may race with the
* sample_delay_ns read in dbs_update_util_handler(), but that
* really doesn't matter. If the read returns a value that's
* too big, the sample will be skipped, but the next invocation
* of dbs_update_util_handler() (when the update has been
* completed) will take a sample.
*
* If this runs in parallel with dbs_work_handler(), we may end
* up overwriting the sample_delay_ns value that it has just
* written, but it will be corrected next time a sample is
* taken, so it shouldn't be significant.
*/
gov_update_sample_delay(policy_dbs, 0);
mutex_unlock(&policy_dbs->update_mutex);
}
return count;
}
EXPORT_SYMBOL_GPL(store_sampling_rate);
/**
* gov_update_cpu_data - Update CPU load data.
* @dbs_data: Top-level governor data pointer.
*
* Update CPU load data for all CPUs in the domain governed by @dbs_data
* (that may be a single policy or a bunch of them if governor tunables are
* system-wide).
*
* Call under the @dbs_data mutex.
*/
void gov_update_cpu_data(struct dbs_data *dbs_data)
{
struct policy_dbs_info *policy_dbs;
list_for_each_entry(policy_dbs, &dbs_data->attr_set.policy_list, list) {
unsigned int j;
for_each_cpu(j, policy_dbs->policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time,
dbs_data->io_is_busy);
if (dbs_data->ignore_nice_load)
j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
}
}
}
EXPORT_SYMBOL_GPL(gov_update_cpu_data);
unsigned int dbs_update(struct cpufreq_policy *policy)
{
struct policy_dbs_info *policy_dbs = policy->governor_data;
struct dbs_data *dbs_data = policy_dbs->dbs_data;
unsigned int ignore_nice = dbs_data->ignore_nice_load;
unsigned int max_load = 0, idle_periods = UINT_MAX;
unsigned int sampling_rate, io_busy, j;
/*
* Sometimes governors may use an additional multiplier to increase
* sample delays temporarily. Apply that multiplier to sampling_rate
* so as to keep the wake-up-from-idle detection logic a bit
* conservative.
*/
sampling_rate = dbs_data->sampling_rate * policy_dbs->rate_mult;
/*
* For the purpose of ondemand, waiting for disk IO is an indication
* that you're performance critical, and not that the system is actually
* idle, so do not add the iowait time to the CPU idle time then.
*/
io_busy = dbs_data->io_is_busy;
/* Get Absolute Load */
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
u64 update_time, cur_idle_time;
unsigned int idle_time, time_elapsed;
unsigned int load;
cur_idle_time = get_cpu_idle_time(j, &update_time, io_busy);
time_elapsed = update_time - j_cdbs->prev_update_time;
j_cdbs->prev_update_time = update_time;
idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
j_cdbs->prev_cpu_idle = cur_idle_time;
if (ignore_nice) {
u64 cur_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
idle_time += div_u64(cur_nice - j_cdbs->prev_cpu_nice, NSEC_PER_USEC);
j_cdbs->prev_cpu_nice = cur_nice;
}
if (unlikely(!time_elapsed)) {
/*
* That can only happen when this function is called
* twice in a row with a very short interval between the
* calls, so the previous load value can be used then.
*/
load = j_cdbs->prev_load;
} else if (unlikely((int)idle_time > 2 * sampling_rate &&
j_cdbs->prev_load)) {
/*
* If the CPU had gone completely idle and a task has
* just woken up on this CPU now, it would be unfair to
* calculate 'load' the usual way for this elapsed
* time-window, because it would show near-zero load,
* irrespective of how CPU intensive that task actually
* was. This is undesirable for latency-sensitive bursty
* workloads.
*
* To avoid this, reuse the 'load' from the previous
* time-window and give this task a chance to start with
* a reasonably high CPU frequency. However, that
* shouldn't be over-done, lest we get stuck at a high
* load (high frequency) for too long, even when the
* current system load has actually dropped down, so
* clear prev_load to guarantee that the load will be
* computed again next time.
*
* Detecting this situation is easy: an unusually large
* 'idle_time' (as compared to the sampling rate)
* indicates this scenario.
*/
load = j_cdbs->prev_load;
j_cdbs->prev_load = 0;
} else {
if (time_elapsed >= idle_time) {
load = 100 * (time_elapsed - idle_time) / time_elapsed;
} else {
/*
* That can happen if idle_time is returned by
* get_cpu_idle_time_jiffy(). In that case
* idle_time is roughly equal to the difference
* between time_elapsed and "busy time" obtained
* from CPU statistics. Then, the "busy time"
* can end up being greater than time_elapsed
* (for example, if jiffies_64 and the CPU
* statistics are updated by different CPUs),
* so idle_time may in fact be negative. That
* means, though, that the CPU was busy all
* the time (on the rough average) during the
* last sampling interval and 100 can be
* returned as the load.
*/
load = (int)idle_time < 0 ? 100 : 0;
}
j_cdbs->prev_load = load;
}
if (unlikely((int)idle_time > 2 * sampling_rate)) {
unsigned int periods = idle_time / sampling_rate;
if (periods < idle_periods)
idle_periods = periods;
}
if (load > max_load)
max_load = load;
}
policy_dbs->idle_periods = idle_periods;
return max_load;
}
EXPORT_SYMBOL_GPL(dbs_update);
static void dbs_work_handler(struct work_struct *work)
{
struct policy_dbs_info *policy_dbs;
struct cpufreq_policy *policy;
struct dbs_governor *gov;
policy_dbs = container_of(work, struct policy_dbs_info, work);
policy = policy_dbs->policy;
gov = dbs_governor_of(policy);
/*
* Make sure cpufreq_governor_limits() isn't evaluating load or the
* ondemand governor isn't updating the sampling rate in parallel.
*/
mutex_lock(&policy_dbs->update_mutex);
gov_update_sample_delay(policy_dbs, gov->gov_dbs_update(policy));
mutex_unlock(&policy_dbs->update_mutex);
/* Allow the utilization update handler to queue up more work. */
atomic_set(&policy_dbs->work_count, 0);
/*
* If the update below is reordered with respect to the sample delay
* modification, the utilization update handler may end up using a stale
* sample delay value.
*/
smp_wmb();
policy_dbs->work_in_progress = false;
}
static void dbs_irq_work(struct irq_work *irq_work)
{
struct policy_dbs_info *policy_dbs;
policy_dbs = container_of(irq_work, struct policy_dbs_info, irq_work);
schedule_work_on(smp_processor_id(), &policy_dbs->work);
}
static void dbs_update_util_handler(struct update_util_data *data, u64 time,
unsigned int flags)
{
struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info, update_util);
struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
u64 delta_ns, lst;
if (!cpufreq_this_cpu_can_update(policy_dbs->policy))
return;
/*
* The work may not be allowed to be queued up right now.
* Possible reasons:
* - Work has already been queued up or is in progress.
* - It is too early (too little time from the previous sample).
*/
if (policy_dbs->work_in_progress)
return;
/*
* If the reads below are reordered before the check above, the value
* of sample_delay_ns used in the computation may be stale.
*/
smp_rmb();
lst = READ_ONCE(policy_dbs->last_sample_time);
delta_ns = time - lst;
if ((s64)delta_ns < policy_dbs->sample_delay_ns)
return;
/*
* If the policy is not shared, the irq_work may be queued up right away
* at this point. Otherwise, we need to ensure that only one of the
* CPUs sharing the policy will do that.
*/
if (policy_dbs->is_shared) {
if (!atomic_add_unless(&policy_dbs->work_count, 1, 1))
return;
/*
* If another CPU updated last_sample_time in the meantime, we
* shouldn't be here, so clear the work counter and bail out.
*/
if (unlikely(lst != READ_ONCE(policy_dbs->last_sample_time))) {
atomic_set(&policy_dbs->work_count, 0);
return;
}
}
policy_dbs->last_sample_time = time;
policy_dbs->work_in_progress = true;
irq_work_queue(&policy_dbs->irq_work);
}
static void gov_set_update_util(struct policy_dbs_info *policy_dbs,
unsigned int delay_us)
{
struct cpufreq_policy *policy = policy_dbs->policy;
int cpu;
gov_update_sample_delay(policy_dbs, delay_us);
policy_dbs->last_sample_time = 0;
for_each_cpu(cpu, policy->cpus) {
struct cpu_dbs_info *cdbs = &per_cpu(cpu_dbs, cpu);
cpufreq_add_update_util_hook(cpu, &cdbs->update_util,
dbs_update_util_handler);
}
}
static inline void gov_clear_update_util(struct cpufreq_policy *policy)
{
int i;
for_each_cpu(i, policy->cpus)
cpufreq_remove_update_util_hook(i);
synchronize_rcu();
}
static struct policy_dbs_info *alloc_policy_dbs_info(struct cpufreq_policy *policy,
struct dbs_governor *gov)
{
struct policy_dbs_info *policy_dbs;
int j;
/* Allocate memory for per-policy governor data. */
policy_dbs = gov->alloc();
if (!policy_dbs)
return NULL;
policy_dbs->policy = policy;
mutex_init(&policy_dbs->update_mutex);
atomic_set(&policy_dbs->work_count, 0);
init_irq_work(&policy_dbs->irq_work, dbs_irq_work);
INIT_WORK(&policy_dbs->work, dbs_work_handler);
/* Set policy_dbs for all CPUs, online+offline */
for_each_cpu(j, policy->related_cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
j_cdbs->policy_dbs = policy_dbs;
}
return policy_dbs;
}
static void free_policy_dbs_info(struct policy_dbs_info *policy_dbs,
struct dbs_governor *gov)
{
int j;
mutex_destroy(&policy_dbs->update_mutex);
for_each_cpu(j, policy_dbs->policy->related_cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
j_cdbs->policy_dbs = NULL;
j_cdbs->update_util.func = NULL;
}
gov->free(policy_dbs);
}
int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
{
struct dbs_governor *gov = dbs_governor_of(policy);
struct dbs_data *dbs_data;
struct policy_dbs_info *policy_dbs;
int ret = 0;
/* State should be equivalent to EXIT */
if (policy->governor_data)
return -EBUSY;
policy_dbs = alloc_policy_dbs_info(policy, gov);
if (!policy_dbs)
return -ENOMEM;
/* Protect gov->gdbs_data against concurrent updates. */
mutex_lock(&gov_dbs_data_mutex);
dbs_data = gov->gdbs_data;
if (dbs_data) {
if (WARN_ON(have_governor_per_policy())) {
ret = -EINVAL;
goto free_policy_dbs_info;
}
policy_dbs->dbs_data = dbs_data;
policy->governor_data = policy_dbs;
gov_attr_set_get(&dbs_data->attr_set, &policy_dbs->list);
goto out;
}
dbs_data = kzalloc(sizeof(*dbs_data), GFP_KERNEL);
if (!dbs_data) {
ret = -ENOMEM;
goto free_policy_dbs_info;
}
gov_attr_set_init(&dbs_data->attr_set, &policy_dbs->list);
ret = gov->init(dbs_data);
if (ret)
goto free_policy_dbs_info;
/*
* The sampling interval should not be less than the transition latency
* of the CPU and it also cannot be too small for dbs_update() to work
* correctly.
*/
dbs_data->sampling_rate = max_t(unsigned int,
CPUFREQ_DBS_MIN_SAMPLING_INTERVAL,
cpufreq_policy_transition_delay_us(policy));
if (!have_governor_per_policy())
gov->gdbs_data = dbs_data;
policy_dbs->dbs_data = dbs_data;
policy->governor_data = policy_dbs;
gov->kobj_type.sysfs_ops = &governor_sysfs_ops;
ret = kobject_init_and_add(&dbs_data->attr_set.kobj, &gov->kobj_type,
get_governor_parent_kobj(policy),
"%s", gov->gov.name);
if (!ret)
goto out;
/* Failure, so roll back. */
pr_err("initialization failed (dbs_data kobject init error %d)\n", ret);
policy->governor_data = NULL;
if (!have_governor_per_policy())
gov->gdbs_data = NULL;
gov->exit(dbs_data);
kfree(dbs_data);
free_policy_dbs_info:
free_policy_dbs_info(policy_dbs, gov);
out:
mutex_unlock(&gov_dbs_data_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_init);
void cpufreq_dbs_governor_exit(struct cpufreq_policy *policy)
{
struct dbs_governor *gov = dbs_governor_of(policy);
struct policy_dbs_info *policy_dbs = policy->governor_data;
struct dbs_data *dbs_data = policy_dbs->dbs_data;
unsigned int count;
/* Protect gov->gdbs_data against concurrent updates. */
mutex_lock(&gov_dbs_data_mutex);
count = gov_attr_set_put(&dbs_data->attr_set, &policy_dbs->list);
policy->governor_data = NULL;
if (!count) {
if (!have_governor_per_policy())
gov->gdbs_data = NULL;
gov->exit(dbs_data);
kfree(dbs_data);
}
free_policy_dbs_info(policy_dbs, gov);
mutex_unlock(&gov_dbs_data_mutex);
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_exit);
int cpufreq_dbs_governor_start(struct cpufreq_policy *policy)
{
struct dbs_governor *gov = dbs_governor_of(policy);
struct policy_dbs_info *policy_dbs = policy->governor_data;
struct dbs_data *dbs_data = policy_dbs->dbs_data;
unsigned int sampling_rate, ignore_nice, j;
unsigned int io_busy;
if (!policy->cur)
return -EINVAL;
policy_dbs->is_shared = policy_is_shared(policy);
policy_dbs->rate_mult = 1;
sampling_rate = dbs_data->sampling_rate;
ignore_nice = dbs_data->ignore_nice_load;
io_busy = dbs_data->io_is_busy;
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time, io_busy);
/*
* Make the first invocation of dbs_update() compute the load.
*/
j_cdbs->prev_load = 0;
if (ignore_nice)
j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
}
gov->start(policy);
gov_set_update_util(policy_dbs, sampling_rate);
return 0;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_start);
void cpufreq_dbs_governor_stop(struct cpufreq_policy *policy)
{
struct policy_dbs_info *policy_dbs = policy->governor_data;
gov_clear_update_util(policy_dbs->policy);
irq_work_sync(&policy_dbs->irq_work);
cancel_work_sync(&policy_dbs->work);
atomic_set(&policy_dbs->work_count, 0);
policy_dbs->work_in_progress = false;
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_stop);
void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy)
{
struct policy_dbs_info *policy_dbs;
/* Protect gov->gdbs_data against cpufreq_dbs_governor_exit() */
mutex_lock(&gov_dbs_data_mutex);
policy_dbs = policy->governor_data;
if (!policy_dbs)
goto out;
mutex_lock(&policy_dbs->update_mutex);
cpufreq_policy_apply_limits(policy);
gov_update_sample_delay(policy_dbs, 0);
mutex_unlock(&policy_dbs->update_mutex);
out:
mutex_unlock(&gov_dbs_data_mutex);
}
EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_limits);