linux/drivers/cpufreq/cpufreq_governor.c
Rafael J. Wysocki 9485e4ca0b cpufreq: governor: Fix handling of special cases in dbs_update()
As reported in KBZ 69821:

"With CONFIG_HZ_PERIODIC=y cpu stays at the lowest frequcency 800MHz
 even if usage goes to 100%, frequency does not scale up, the governor
 in use is ondemand. Neither works conservative. Performance and
 userspace governors work as expected.

 With CONFIG_NO_HZ_IDLE or CONFIG_NO_HZ_FULL cpu scales up with ondemand
 as expected."

Analysis carried out by Chen Yu leads to the conclusion that the
observed issue is due to idle_time in dbs_update() representing a
negative number in which case the function will return 0 as the load
(unless load is greater than 0 for another CPU sharing the policy),
although that need not be the right choice.

Indeed, idle_time representing a negative number means that during
the last sampling interval the CPU was almost 100% busy on the rough
average, so 100 should be returned as the load in that case.

Modify the code accordingly and rearrange it to clarify the handling
of all of the special cases in it.  While at it, also avoid returning
zero as the load if time_elapsed is 0 (it doesn't really make sense
to return 0 then).

Link: https://bugzilla.kernel.org/show_bug.cgi?id=69821
Tested-by: Chen Yu <yu.c.chen@intel.com>
Tested-by: Timo Valtoaho <timo.valtoaho@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
2016-05-06 14:24:23 +02:00

586 lines
17 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/sched.h>
#include <linux/slab.h>
#include "cpufreq_governor.h"
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 rate;
int ret;
ret = sscanf(buf, "%u", &rate);
if (ret != 1)
return -EINVAL;
dbs_data->sampling_rate = max(rate, dbs_data->min_sampling_rate);
/*
* 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->timer_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->timer_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;
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 += cputime_to_usecs(cur_nice - j_cdbs->prev_cpu_nice);
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(time_elapsed > 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: the governor's
* utilization update handler would not have run during
* CPU-idle periods. Hence, an unusually large
* 'time_elapsed' (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 (load > max_load)
max_load = load;
}
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->timer_mutex);
gov_update_sample_delay(policy_dbs, gov->gov_dbs_timer(policy));
mutex_unlock(&policy_dbs->timer_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 long util, unsigned long max)
{
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;
/*
* 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_sched();
}
static void gov_cancel_work(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;
}
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->timer_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->timer_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);
}
static int cpufreq_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;
unsigned int latency;
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, !policy->governor->initialized);
if (ret)
goto free_policy_dbs_info;
/* policy latency is in ns. Convert it to us first */
latency = policy->cpuinfo.transition_latency / 1000;
if (latency == 0)
latency = 1;
/* Bring kernel and HW constraints together */
dbs_data->min_sampling_rate = max(dbs_data->min_sampling_rate,
MIN_LATENCY_MULTIPLIER * latency);
dbs_data->sampling_rate = max(dbs_data->min_sampling_rate,
LATENCY_MULTIPLIER * latency);
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("cpufreq: Governor 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, !policy->governor->initialized);
kfree(dbs_data);
free_policy_dbs_info:
free_policy_dbs_info(policy_dbs, gov);
out:
mutex_unlock(&gov_dbs_data_mutex);
return ret;
}
static int cpufreq_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, policy->governor->initialized == 1);
kfree(dbs_data);
}
free_policy_dbs_info(policy_dbs, gov);
mutex_unlock(&gov_dbs_data_mutex);
return 0;
}
static int cpufreq_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;
}
static int cpufreq_governor_stop(struct cpufreq_policy *policy)
{
gov_cancel_work(policy);
return 0;
}
static int cpufreq_governor_limits(struct cpufreq_policy *policy)
{
struct policy_dbs_info *policy_dbs = policy->governor_data;
mutex_lock(&policy_dbs->timer_mutex);
if (policy->max < policy->cur)
__cpufreq_driver_target(policy, policy->max, CPUFREQ_RELATION_H);
else if (policy->min > policy->cur)
__cpufreq_driver_target(policy, policy->min, CPUFREQ_RELATION_L);
gov_update_sample_delay(policy_dbs, 0);
mutex_unlock(&policy_dbs->timer_mutex);
return 0;
}
int cpufreq_governor_dbs(struct cpufreq_policy *policy, unsigned int event)
{
if (event == CPUFREQ_GOV_POLICY_INIT) {
return cpufreq_governor_init(policy);
} else if (policy->governor_data) {
switch (event) {
case CPUFREQ_GOV_POLICY_EXIT:
return cpufreq_governor_exit(policy);
case CPUFREQ_GOV_START:
return cpufreq_governor_start(policy);
case CPUFREQ_GOV_STOP:
return cpufreq_governor_stop(policy);
case CPUFREQ_GOV_LIMITS:
return cpufreq_governor_limits(policy);
}
}
return -EINVAL;
}
EXPORT_SYMBOL_GPL(cpufreq_governor_dbs);