[deliverable/linux.git] / drivers / cpufreq / cpufreq_ondemand.c

/*
 *  drivers/cpufreq/cpufreq_ondemand.c
 *
 *  Copyright (C)  2001 Russell King
 *            (C)  2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
 *                      Jun Nakajima <jun.nakajima@intel.com>
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/cpufreq.h>
#include <linux/cpu.h>
#include <linux/jiffies.h>
#include <linux/kernel_stat.h>
#include <linux/mutex.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/ktime.h>
#include <linux/sched.h>

/*
 * dbs is used in this file as a shortform for demandbased switching
 * It helps to keep variable names smaller, simpler
 */

#define DEF_FREQUENCY_DOWN_DIFFERENTIAL         (10)
#define DEF_FREQUENCY_UP_THRESHOLD              (80)
#define DEF_SAMPLING_DOWN_FACTOR                (1)
#define MAX_SAMPLING_DOWN_FACTOR                (100000)
#define MICRO_FREQUENCY_DOWN_DIFFERENTIAL       (3)
#define MICRO_FREQUENCY_UP_THRESHOLD            (95)
#define MICRO_FREQUENCY_MIN_SAMPLE_RATE         (10000)
#define MIN_FREQUENCY_UP_THRESHOLD              (11)
#define MAX_FREQUENCY_UP_THRESHOLD              (100)

/*
 * The polling frequency of this governor depends on the capability of
 * the processor. Default polling frequency is 1000 times the transition
 * latency of the processor. The governor will work on any processor with
 * transition latency <= 10mS, using appropriate sampling
 * rate.
 * For CPUs with transition latency > 10mS (mostly drivers with CPUFREQ_ETERNAL)
 * this governor will not work.
 * All times here are in uS.
 */
#define MIN_SAMPLING_RATE_RATIO                 (2)

static unsigned int min_sampling_rate;

#define LATENCY_MULTIPLIER                      (1000)
#define MIN_LATENCY_MULTIPLIER                  (100)
#define TRANSITION_LATENCY_LIMIT                (10 * 1000 * 1000)

static void do_dbs_timer(struct work_struct *work);
static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                                unsigned int event);

#ifndef CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND
static
#endif
struct cpufreq_governor cpufreq_gov_ondemand = {
       .name                   = "ondemand",
       .governor               = cpufreq_governor_dbs,
       .max_transition_latency = TRANSITION_LATENCY_LIMIT,
       .owner                  = THIS_MODULE,
};

/* Sampling types */
enum {DBS_NORMAL_SAMPLE, DBS_SUB_SAMPLE};

struct cpu_dbs_info_s {
        cputime64_t prev_cpu_idle;
        cputime64_t prev_cpu_iowait;
        cputime64_t prev_cpu_wall;
        cputime64_t prev_cpu_nice;
        struct cpufreq_policy *cur_policy;
        struct delayed_work work;
        struct cpufreq_frequency_table *freq_table;
        unsigned int freq_lo;
        unsigned int freq_lo_jiffies;
        unsigned int freq_hi_jiffies;
        unsigned int rate_mult;
        int cpu;
        unsigned int sample_type:1;
        /*
         * percpu mutex that serializes governor limit change with
         * do_dbs_timer invocation. We do not want do_dbs_timer to run
         * when user is changing the governor or limits.
         */
        struct mutex timer_mutex;
};
static DEFINE_PER_CPU(struct cpu_dbs_info_s, od_cpu_dbs_info);

static unsigned int dbs_enable; /* number of CPUs using this policy */

/*
 * dbs_mutex protects dbs_enable in governor start/stop.
 */
static DEFINE_MUTEX(dbs_mutex);

static struct dbs_tuners {
        unsigned int sampling_rate;
        unsigned int up_threshold;
        unsigned int down_differential;
        unsigned int ignore_nice;
        unsigned int sampling_down_factor;
        unsigned int powersave_bias;
        unsigned int io_is_busy;
} dbs_tuners_ins = {
        .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
        .sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR,
        .down_differential = DEF_FREQUENCY_DOWN_DIFFERENTIAL,
        .ignore_nice = 0,
        .powersave_bias = 0,
};

static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
                                                        cputime64_t *wall)
{
        cputime64_t idle_time;
        cputime64_t cur_wall_time;
        cputime64_t busy_time;

        cur_wall_time = jiffies64_to_cputime64(get_jiffies_64());
        busy_time = cputime64_add(kstat_cpu(cpu).cpustat.user,
                        kstat_cpu(cpu).cpustat.system);

        busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.irq);
        busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.softirq);
        busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.steal);
        busy_time = cputime64_add(busy_time, kstat_cpu(cpu).cpustat.nice);

        idle_time = cputime64_sub(cur_wall_time, busy_time);
        if (wall)
                *wall = (cputime64_t)jiffies_to_usecs(cur_wall_time);

        return (cputime64_t)jiffies_to_usecs(idle_time);
}

static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
{
        u64 idle_time = get_cpu_idle_time_us(cpu, NULL);

        if (idle_time == -1ULL)
                return get_cpu_idle_time_jiffy(cpu, wall);
        else
                idle_time += get_cpu_iowait_time_us(cpu, wall);

        return idle_time;
}

static inline cputime64_t get_cpu_iowait_time(unsigned int cpu, cputime64_t *wall)
{
        u64 iowait_time = get_cpu_iowait_time_us(cpu, wall);

        if (iowait_time == -1ULL)
                return 0;

        return iowait_time;
}

/*
 * Find right freq to be set now with powersave_bias on.
 * Returns the freq_hi to be used right now and will set freq_hi_jiffies,
 * freq_lo, and freq_lo_jiffies in percpu area for averaging freqs.
 */
static unsigned int powersave_bias_target(struct cpufreq_policy *policy,
                                          unsigned int freq_next,
                                          unsigned int relation)
{
        unsigned int freq_req, freq_reduc, freq_avg;
        unsigned int freq_hi, freq_lo;
        unsigned int index = 0;
        unsigned int jiffies_total, jiffies_hi, jiffies_lo;
        struct cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info,
                                                   policy->cpu);

        if (!dbs_info->freq_table) {
                dbs_info->freq_lo = 0;
                dbs_info->freq_lo_jiffies = 0;
                return freq_next;
        }

        cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_next,
                        relation, &index);
        freq_req = dbs_info->freq_table[index].frequency;
        freq_reduc = freq_req * dbs_tuners_ins.powersave_bias / 1000;
        freq_avg = freq_req - freq_reduc;

        /* Find freq bounds for freq_avg in freq_table */
        index = 0;
        cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
                        CPUFREQ_RELATION_H, &index);
        freq_lo = dbs_info->freq_table[index].frequency;
        index = 0;
        cpufreq_frequency_table_target(policy, dbs_info->freq_table, freq_avg,
                        CPUFREQ_RELATION_L, &index);
        freq_hi = dbs_info->freq_table[index].frequency;

        /* Find out how long we have to be in hi and lo freqs */
        if (freq_hi == freq_lo) {
                dbs_info->freq_lo = 0;
                dbs_info->freq_lo_jiffies = 0;
                return freq_lo;
        }
        jiffies_total = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
        jiffies_hi = (freq_avg - freq_lo) * jiffies_total;
        jiffies_hi += ((freq_hi - freq_lo) / 2);
        jiffies_hi /= (freq_hi - freq_lo);
        jiffies_lo = jiffies_total - jiffies_hi;
        dbs_info->freq_lo = freq_lo;
        dbs_info->freq_lo_jiffies = jiffies_lo;
        dbs_info->freq_hi_jiffies = jiffies_hi;
        return freq_hi;
}

static void ondemand_powersave_bias_init_cpu(int cpu)
{
        struct cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
        dbs_info->freq_table = cpufreq_frequency_get_table(cpu);
        dbs_info->freq_lo = 0;
}

static void ondemand_powersave_bias_init(void)
{
        int i;
        for_each_online_cpu(i) {
                ondemand_powersave_bias_init_cpu(i);
        }
}

/************************** sysfs interface ************************/

static ssize_t show_sampling_rate_min(struct kobject *kobj,
                                      struct attribute *attr, char *buf)
{
        return sprintf(buf, "%u\n", min_sampling_rate);
}

define_one_global_ro(sampling_rate_min);

/* cpufreq_ondemand Governor Tunables */
#define show_one(file_name, object)                                     \
static ssize_t show_##file_name                                         \
(struct kobject *kobj, struct attribute *attr, char *buf)              \
{                                                                       \
        return sprintf(buf, "%u\n", dbs_tuners_ins.object);             \
}
show_one(sampling_rate, sampling_rate);
show_one(io_is_busy, io_is_busy);
show_one(up_threshold, up_threshold);
show_one(sampling_down_factor, sampling_down_factor);
show_one(ignore_nice_load, ignore_nice);
show_one(powersave_bias, powersave_bias);

static ssize_t store_sampling_rate(struct kobject *a, struct attribute *b,
                                   const char *buf, size_t count)
{
        unsigned int input;
        int ret;
        ret = sscanf(buf, "%u", &input);
        if (ret != 1)
                return -EINVAL;
        dbs_tuners_ins.sampling_rate = max(input, min_sampling_rate);
        return count;
}

static ssize_t store_io_is_busy(struct kobject *a, struct attribute *b,
                                   const char *buf, size_t count)
{
        unsigned int input;
        int ret;

        ret = sscanf(buf, "%u", &input);
        if (ret != 1)
                return -EINVAL;
        dbs_tuners_ins.io_is_busy = !!input;
        return count;
}

static ssize_t store_up_threshold(struct kobject *a, struct attribute *b,
                                  const char *buf, size_t count)
{
        unsigned int input;
        int ret;
        ret = sscanf(buf, "%u", &input);

        if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD ||
                        input < MIN_FREQUENCY_UP_THRESHOLD) {
                return -EINVAL;
        }
        dbs_tuners_ins.up_threshold = input;
        return count;
}

static ssize_t store_sampling_down_factor(struct kobject *a,
                        struct attribute *b, const char *buf, size_t count)
{
        unsigned int input, j;
        int ret;
        ret = sscanf(buf, "%u", &input);

        if (ret != 1 || input > MAX_SAMPLING_DOWN_FACTOR || input < 1)
                return -EINVAL;
        dbs_tuners_ins.sampling_down_factor = input;

        /* Reset down sampling multiplier in case it was active */
        for_each_online_cpu(j) {
                struct cpu_dbs_info_s *dbs_info;
                dbs_info = &per_cpu(od_cpu_dbs_info, j);
                dbs_info->rate_mult = 1;
        }
        return count;
}

static ssize_t store_ignore_nice_load(struct kobject *a, struct attribute *b,
                                      const char *buf, size_t count)
{
        unsigned int input;
        int ret;

        unsigned int j;

        ret = sscanf(buf, "%u", &input);
        if (ret != 1)
                return -EINVAL;

        if (input > 1)
                input = 1;

        if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */
                return count;
        }
        dbs_tuners_ins.ignore_nice = input;

        /* we need to re-evaluate prev_cpu_idle */
        for_each_online_cpu(j) {
                struct cpu_dbs_info_s *dbs_info;
                dbs_info = &per_cpu(od_cpu_dbs_info, j);
                dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
                                                &dbs_info->prev_cpu_wall);
                if (dbs_tuners_ins.ignore_nice)
                        dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;

        }
        return count;
}

static ssize_t store_powersave_bias(struct kobject *a, struct attribute *b,
                                    const char *buf, size_t count)
{
        unsigned int input;
        int ret;
        ret = sscanf(buf, "%u", &input);

        if (ret != 1)
                return -EINVAL;

        if (input > 1000)
                input = 1000;

        dbs_tuners_ins.powersave_bias = input;
        ondemand_powersave_bias_init();
        return count;
}

define_one_global_rw(sampling_rate);
define_one_global_rw(io_is_busy);
define_one_global_rw(up_threshold);
define_one_global_rw(sampling_down_factor);
define_one_global_rw(ignore_nice_load);
define_one_global_rw(powersave_bias);

static struct attribute *dbs_attributes[] = {
        &sampling_rate_min.attr,
        &sampling_rate.attr,
        &up_threshold.attr,
        &sampling_down_factor.attr,
        &ignore_nice_load.attr,
        &powersave_bias.attr,
        &io_is_busy.attr,
        NULL
};

static struct attribute_group dbs_attr_group = {
        .attrs = dbs_attributes,
        .name = "ondemand",
};

/************************** sysfs end ************************/

static void dbs_freq_increase(struct cpufreq_policy *p, unsigned int freq)
{
        if (dbs_tuners_ins.powersave_bias)
                freq = powersave_bias_target(p, freq, CPUFREQ_RELATION_H);
        else if (p->cur == p->max)
                return;

        __cpufreq_driver_target(p, freq, dbs_tuners_ins.powersave_bias ?
                        CPUFREQ_RELATION_L : CPUFREQ_RELATION_H);
}

static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
{
        unsigned int max_load_freq;

        struct cpufreq_policy *policy;
        unsigned int j;

        this_dbs_info->freq_lo = 0;
        policy = this_dbs_info->cur_policy;

        /*
         * Every sampling_rate, we check, if current idle time is less
         * than 20% (default), then we try to increase frequency
         * Every sampling_rate, we look for a the lowest
         * frequency which can sustain the load while keeping idle time over
         * 30%. If such a frequency exist, we try to decrease to this frequency.
         *
         * Any frequency increase takes it to the maximum frequency.
         * Frequency reduction happens at minimum steps of
         * 5% (default) of current frequency
         */

        /* Get Absolute Load - in terms of freq */
        max_load_freq = 0;

        for_each_cpu(j, policy->cpus) {
                struct cpu_dbs_info_s *j_dbs_info;
                cputime64_t cur_wall_time, cur_idle_time, cur_iowait_time;
                unsigned int idle_time, wall_time, iowait_time;
                unsigned int load, load_freq;
                int freq_avg;

                j_dbs_info = &per_cpu(od_cpu_dbs_info, j);

                cur_idle_time = get_cpu_idle_time(j, &cur_wall_time);
                cur_iowait_time = get_cpu_iowait_time(j, &cur_wall_time);

                wall_time = (unsigned int) cputime64_sub(cur_wall_time,
                                j_dbs_info->prev_cpu_wall);
                j_dbs_info->prev_cpu_wall = cur_wall_time;

                idle_time = (unsigned int) cputime64_sub(cur_idle_time,
                                j_dbs_info->prev_cpu_idle);
                j_dbs_info->prev_cpu_idle = cur_idle_time;

                iowait_time = (unsigned int) cputime64_sub(cur_iowait_time,
                                j_dbs_info->prev_cpu_iowait);
                j_dbs_info->prev_cpu_iowait = cur_iowait_time;

                if (dbs_tuners_ins.ignore_nice) {
                        cputime64_t cur_nice;
                        unsigned long cur_nice_jiffies;

                        cur_nice = cputime64_sub(kstat_cpu(j).cpustat.nice,
                                         j_dbs_info->prev_cpu_nice);
                        /*
                         * Assumption: nice time between sampling periods will
                         * be less than 2^32 jiffies for 32 bit sys
                         */
                        cur_nice_jiffies = (unsigned long)
                                        cputime64_to_jiffies64(cur_nice);

                        j_dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice;
                        idle_time += jiffies_to_usecs(cur_nice_jiffies);
                }

                /*
                 * 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 subtract the iowait time
                 * from the cpu idle time.
                 */

                if (dbs_tuners_ins.io_is_busy && idle_time >= iowait_time)
                        idle_time -= iowait_time;

                if (unlikely(!wall_time || wall_time < idle_time))
                        continue;

                load = 100 * (wall_time - idle_time) / wall_time;

                freq_avg = __cpufreq_driver_getavg(policy, j);
                if (freq_avg <= 0)
                        freq_avg = policy->cur;

                load_freq = load * freq_avg;
                if (load_freq > max_load_freq)
                        max_load_freq = load_freq;
        }

        /* Check for frequency increase */
        if (max_load_freq > dbs_tuners_ins.up_threshold * policy->cur) {
                /* If switching to max speed, apply sampling_down_factor */
                if (policy->cur < policy->max)
                        this_dbs_info->rate_mult =
                                dbs_tuners_ins.sampling_down_factor;
                dbs_freq_increase(policy, policy->max);
                return;
        }

        /* Check for frequency decrease */
        /* if we cannot reduce the frequency anymore, break out early */
        if (policy->cur == policy->min)
                return;

        /*
         * The optimal frequency is the frequency that is the lowest that
         * can support the current CPU usage without triggering the up
         * policy. To be safe, we focus 10 points under the threshold.
         */
        if (max_load_freq <
            (dbs_tuners_ins.up_threshold - dbs_tuners_ins.down_differential) *
             policy->cur) {
                unsigned int freq_next;
                freq_next = max_load_freq /
                                (dbs_tuners_ins.up_threshold -
                                 dbs_tuners_ins.down_differential);

                /* No longer fully busy, reset rate_mult */
                this_dbs_info->rate_mult = 1;

                if (freq_next < policy->min)
                        freq_next = policy->min;

                if (!dbs_tuners_ins.powersave_bias) {
                        __cpufreq_driver_target(policy, freq_next,
                                        CPUFREQ_RELATION_L);
                } else {
                        int freq = powersave_bias_target(policy, freq_next,
                                        CPUFREQ_RELATION_L);
                        __cpufreq_driver_target(policy, freq,
                                CPUFREQ_RELATION_L);
                }
        }
}

static void do_dbs_timer(struct work_struct *work)
{
        struct cpu_dbs_info_s *dbs_info =
                container_of(work, struct cpu_dbs_info_s, work.work);
        unsigned int cpu = dbs_info->cpu;
        int sample_type = dbs_info->sample_type;

        int delay;

        mutex_lock(&dbs_info->timer_mutex);

        /* Common NORMAL_SAMPLE setup */
        dbs_info->sample_type = DBS_NORMAL_SAMPLE;
        if (!dbs_tuners_ins.powersave_bias ||
            sample_type == DBS_NORMAL_SAMPLE) {
                dbs_check_cpu(dbs_info);
                if (dbs_info->freq_lo) {
                        /* Setup timer for SUB_SAMPLE */
                        dbs_info->sample_type = DBS_SUB_SAMPLE;
                        delay = dbs_info->freq_hi_jiffies;
                } else {
                        /* We want all CPUs to do sampling nearly on
                         * same jiffy
                         */
                        delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate
                                * dbs_info->rate_mult);

                        if (num_online_cpus() > 1)
                                delay -= jiffies % delay;
                }
        } else {
                __cpufreq_driver_target(dbs_info->cur_policy,
                        dbs_info->freq_lo, CPUFREQ_RELATION_H);
                delay = dbs_info->freq_lo_jiffies;
        }
        schedule_delayed_work_on(cpu, &dbs_info->work, delay);
        mutex_unlock(&dbs_info->timer_mutex);
}

static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
{
        /* We want all CPUs to do sampling nearly on same jiffy */
        int delay = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);

        if (num_online_cpus() > 1)
                delay -= jiffies % delay;

        dbs_info->sample_type = DBS_NORMAL_SAMPLE;
        INIT_DELAYED_WORK_DEFERRABLE(&dbs_info->work, do_dbs_timer);
        schedule_delayed_work_on(dbs_info->cpu, &dbs_info->work, delay);
}

static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
{
        cancel_delayed_work_sync(&dbs_info->work);
}

/*
 * Not all CPUs want IO time to be accounted as busy; this dependson how
 * efficient idling at a higher frequency/voltage is.
 * Pavel Machek says this is not so for various generations of AMD and old
 * Intel systems.
 * Mike Chan (androidlcom) calis this is also not true for ARM.
 * Because of this, whitelist specific known (series) of CPUs by default, and
 * leave all others up to the user.
 */
static int should_io_be_busy(void)
{
#if defined(CONFIG_X86)
        /*
         * For Intel, Core 2 (model 15) andl later have an efficient idle.
         */
        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
            boot_cpu_data.x86 == 6 &&
            boot_cpu_data.x86_model >= 15)
                return 1;
#endif
        return 0;
}

static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                                   unsigned int event)
{
        unsigned int cpu = policy->cpu;
        struct cpu_dbs_info_s *this_dbs_info;
        unsigned int j;
        int rc;

        this_dbs_info = &per_cpu(od_cpu_dbs_info, cpu);

        switch (event) {
        case CPUFREQ_GOV_START:
                if ((!cpu_online(cpu)) || (!policy->cur))
                        return -EINVAL;

                mutex_lock(&dbs_mutex);

                dbs_enable++;
                for_each_cpu(j, policy->cpus) {
                        struct cpu_dbs_info_s *j_dbs_info;
                        j_dbs_info = &per_cpu(od_cpu_dbs_info, j);
                        j_dbs_info->cur_policy = policy;

                        j_dbs_info->prev_cpu_idle = get_cpu_idle_time(j,
                                                &j_dbs_info->prev_cpu_wall);
                        if (dbs_tuners_ins.ignore_nice) {
                                j_dbs_info->prev_cpu_nice =
                                                kstat_cpu(j).cpustat.nice;
                        }
                }
                this_dbs_info->cpu = cpu;
                this_dbs_info->rate_mult = 1;
                ondemand_powersave_bias_init_cpu(cpu);
                /*
                 * Start the timerschedule work, when this governor
                 * is used for first time
                 */
                if (dbs_enable == 1) {
                        unsigned int latency;

                        rc = sysfs_create_group(cpufreq_global_kobject,
                                                &dbs_attr_group);
                        if (rc) {
                                mutex_unlock(&dbs_mutex);
                                return rc;
                        }

                        /* 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 */
                        min_sampling_rate = max(min_sampling_rate,
                                        MIN_LATENCY_MULTIPLIER * latency);
                        dbs_tuners_ins.sampling_rate =
                                max(min_sampling_rate,
                                    latency * LATENCY_MULTIPLIER);
                        dbs_tuners_ins.io_is_busy = should_io_be_busy();
                }
                mutex_unlock(&dbs_mutex);

                mutex_init(&this_dbs_info->timer_mutex);
                dbs_timer_init(this_dbs_info);
                break;

        case CPUFREQ_GOV_STOP:
                dbs_timer_exit(this_dbs_info);

                mutex_lock(&dbs_mutex);
                mutex_destroy(&this_dbs_info->timer_mutex);
                dbs_enable--;
                mutex_unlock(&dbs_mutex);
                if (!dbs_enable)
                        sysfs_remove_group(cpufreq_global_kobject,
                                           &dbs_attr_group);

                break;

        case CPUFREQ_GOV_LIMITS:
                mutex_lock(&this_dbs_info->timer_mutex);
                if (policy->max < this_dbs_info->cur_policy->cur)
                        __cpufreq_driver_target(this_dbs_info->cur_policy,
                                policy->max, CPUFREQ_RELATION_H);
                else if (policy->min > this_dbs_info->cur_policy->cur)
                        __cpufreq_driver_target(this_dbs_info->cur_policy,
                                policy->min, CPUFREQ_RELATION_L);
                mutex_unlock(&this_dbs_info->timer_mutex);
                break;
        }
        return 0;
}

static int __init cpufreq_gov_dbs_init(void)
{
        cputime64_t wall;
        u64 idle_time;
        int cpu = get_cpu();

        idle_time = get_cpu_idle_time_us(cpu, &wall);
        put_cpu();
        if (idle_time != -1ULL) {
                /* Idle micro accounting is supported. Use finer thresholds */
                dbs_tuners_ins.up_threshold = MICRO_FREQUENCY_UP_THRESHOLD;
                dbs_tuners_ins.down_differential =
                                        MICRO_FREQUENCY_DOWN_DIFFERENTIAL;
                /*
                 * In nohz/micro accounting case we set the minimum frequency
                 * not depending on HZ, but fixed (very low). The deferred
                 * timer might skip some samples if idle/sleeping as needed.
                */
                min_sampling_rate = MICRO_FREQUENCY_MIN_SAMPLE_RATE;
        } else {
                /* For correct statistics, we need 10 ticks for each measure */
                min_sampling_rate =
                        MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10);
        }

        return cpufreq_register_governor(&cpufreq_gov_ondemand);
}

static void __exit cpufreq_gov_dbs_exit(void)
{
        cpufreq_unregister_governor(&cpufreq_gov_ondemand);
}


MODULE_AUTHOR("Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>");
MODULE_AUTHOR("Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>");
MODULE_DESCRIPTION("'cpufreq_ondemand' - A dynamic cpufreq governor for "
        "Low Latency Frequency Transition capable processors");
MODULE_LICENSE("GPL");

#ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND
fs_initcall(cpufreq_gov_dbs_init);
#else
module_init(cpufreq_gov_dbs_init);
#endif
module_exit(cpufreq_gov_dbs_exit);