/*
 * CPUFreq governor based on scheduler-provided CPU utilization data.
 *
 * Copyright (C) 2016, Intel Corporation
 * Author: Rafael J. Wysocki <rafael.j.wysocki@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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/cpufreq.h>
#include <linux/kthread.h>
#include <uapi/linux/sched/types.h>
#include <linux/slab.h>
#include <trace/events/power.h>

#include "sched.h"

#define SUGOV_KTHREAD_PRIORITY  50

struct sugov_tunables {
        struct gov_attr_set attr_set;
        unsigned int rate_limit_us;
};

struct sugov_policy {
        struct cpufreq_policy *policy;

        struct sugov_tunables *tunables;
        struct list_head tunables_hook;

        raw_spinlock_t update_lock;  /* For shared policies */
        u64 last_freq_update_time;
        s64 freq_update_delay_ns;
        unsigned int next_freq;
        unsigned int cached_raw_freq;

        /* The next fields are only needed if fast switch cannot be used. */
        struct irq_work irq_work;
        struct kthread_work work;
        struct mutex work_lock;
        struct kthread_worker worker;
        struct task_struct *thread;
        bool work_in_progress;

        bool need_freq_update;
};

struct sugov_cpu {
        struct update_util_data update_util;
        struct sugov_policy *sg_policy;

        unsigned long iowait_boost;
        unsigned long iowait_boost_max;
        u64 last_update;

        /* The fields below are only needed when sharing a policy. */
        unsigned long util;
        unsigned long max;
        unsigned int flags;

        /* The field below is for single-CPU policies only. */
#ifdef CONFIG_NO_HZ_COMMON
        unsigned long saved_idle_calls;
#endif
};

static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);

/************************ Governor internals ***********************/

static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
{
        s64 delta_ns;

        if (sg_policy->work_in_progress)
                return false;

        if (unlikely(sg_policy->need_freq_update)) {
                sg_policy->need_freq_update = false;
                /*
                 * This happens when limits change, so forget the previous
                 * next_freq value and force an update.
                 */
                sg_policy->next_freq = UINT_MAX;
                return true;
        }

        delta_ns = time - sg_policy->last_freq_update_time;
        return delta_ns >= sg_policy->freq_update_delay_ns;
}

static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
                                unsigned int next_freq)
{
        struct cpufreq_policy *policy = sg_policy->policy;

        if (sg_policy->next_freq == next_freq)
                return;

        sg_policy->next_freq = next_freq;
        sg_policy->last_freq_update_time = time;

        if (policy->fast_switch_enabled) {
                next_freq = cpufreq_driver_fast_switch(policy, next_freq);
                if (next_freq == CPUFREQ_ENTRY_INVALID)
                        return;

                policy->cur = next_freq;
                trace_cpu_frequency(next_freq, smp_processor_id());
        } else {
                sg_policy->work_in_progress = true;
                irq_work_queue(&sg_policy->irq_work);
        }
}

/**
 * get_next_freq - Compute a new frequency for a given cpufreq policy.
 * @sg_policy: schedutil policy object to compute the new frequency for.
 * @util: Current CPU utilization.
 * @max: CPU capacity.
 *
 * If the utilization is frequency-invariant, choose the new frequency to be
 * proportional to it, that is
 *
 * next_freq = C * max_freq * util / max
 *
 * Otherwise, approximate the would-be frequency-invariant utilization by
 * util_raw * (curr_freq / max_freq) which leads to
 *
 * next_freq = C * curr_freq * util_raw / max
 *
 * Take C = 1.25 for the frequency tipping point at (util / max) = 0.8.
 *
 * The lowest driver-supported frequency which is equal or greater than the raw
 * next_freq (as calculated above) is returned, subject to policy min/max and
 * cpufreq driver limitations.
 */
static unsigned int get_next_freq(struct sugov_policy *sg_policy,
                                  unsigned long util, unsigned long max)
{
        struct cpufreq_policy *policy = sg_policy->policy;
        unsigned int freq = arch_scale_freq_invariant() ?
                                policy->cpuinfo.max_freq : policy->cur;

        freq = (freq + (freq >> 2)) * util / max;

        if (freq == sg_policy->cached_raw_freq && sg_policy->next_freq != UINT_MAX)
                return sg_policy->next_freq;
        sg_policy->cached_raw_freq = freq;
        return cpufreq_driver_resolve_freq(policy, freq);
}

static void sugov_get_util(unsigned long *util, unsigned long *max)
{
        struct rq *rq = this_rq();
        unsigned long cfs_max;

        cfs_max = arch_scale_cpu_capacity(NULL, smp_processor_id());

        *util = min(rq->cfs.avg.util_avg, cfs_max);
        *max = cfs_max;
}

static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
                                   unsigned int flags)
{
        if (flags & SCHED_CPUFREQ_IOWAIT) {
                sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
        } else if (sg_cpu->iowait_boost) {
                s64 delta_ns = time - sg_cpu->last_update;

                /* Clear iowait_boost if the CPU apprears to have been idle. */
                if (delta_ns > TICK_NSEC)
                        sg_cpu->iowait_boost = 0;
        }
}

static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long *util,
                               unsigned long *max)
{
        unsigned long boost_util = sg_cpu->iowait_boost;
        unsigned long boost_max = sg_cpu->iowait_boost_max;

        if (!boost_util)
                return;

        if (*util * boost_max < *max * boost_util) {
                *util = boost_util;
                *max = boost_max;
        }
        sg_cpu->iowait_boost >>= 1;
}

#ifdef CONFIG_NO_HZ_COMMON
static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
{
        unsigned long idle_calls = tick_nohz_get_idle_calls();
        bool ret = idle_calls == sg_cpu->saved_idle_calls;

        sg_cpu->saved_idle_calls = idle_calls;
        return ret;
}
#else
static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
#endif /* CONFIG_NO_HZ_COMMON */

static void sugov_update_single(struct update_util_data *hook, u64 time,
                                unsigned int flags)
{
        struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
        struct sugov_policy *sg_policy = sg_cpu->sg_policy;
        struct cpufreq_policy *policy = sg_policy->policy;
        unsigned long util, max;
        unsigned int next_f;
        bool busy;

        sugov_set_iowait_boost(sg_cpu, time, flags);
        sg_cpu->last_update = time;

        if (!sugov_should_update_freq(sg_policy, time))
                return;

        busy = sugov_cpu_is_busy(sg_cpu);

        if (flags & SCHED_CPUFREQ_RT_DL) {
                next_f = policy->cpuinfo.max_freq;
        } else {
                sugov_get_util(&util, &max);
                sugov_iowait_boost(sg_cpu, &util, &max);
                next_f = get_next_freq(sg_policy, util, max);
                /*
                 * Do not reduce the frequency if the CPU has not been idle
                 * recently, as the reduction is likely to be premature then.
                 */
                if (busy && next_f < sg_policy->next_freq)
                        next_f = sg_policy->next_freq;
        }
        sugov_update_commit(sg_policy, time, next_f);
}

static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
{
        struct sugov_policy *sg_policy = sg_cpu->sg_policy;
        struct cpufreq_policy *policy = sg_policy->policy;
        unsigned long util = 0, max = 1;
        unsigned int j;

        for_each_cpu(j, policy->cpus) {
                struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
                unsigned long j_util, j_max;
                s64 delta_ns;

                /*
                 * If the CPU utilization was last updated before the previous
                 * frequency update and the time elapsed between the last update
                 * of the CPU utilization and the last frequency update is long
                 * enough, don't take the CPU into account as it probably is
                 * idle now (and clear iowait_boost for it).
                 */
                delta_ns = time - j_sg_cpu->last_update;
                if (delta_ns > TICK_NSEC) {
                        j_sg_cpu->iowait_boost = 0;
                        continue;
                }
                if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL)
                        return policy->cpuinfo.max_freq;

                j_util = j_sg_cpu->util;
                j_max = j_sg_cpu->max;
                if (j_util * max > j_max * util) {
                        util = j_util;
                        max = j_max;
                }

                sugov_iowait_boost(j_sg_cpu, &util, &max);
        }

        return get_next_freq(sg_policy, util, max);
}

static void sugov_update_shared(struct update_util_data *hook, u64 time,
                                unsigned int flags)
{
        struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
        struct sugov_policy *sg_policy = sg_cpu->sg_policy;
        unsigned long util, max;
        unsigned int next_f;

        sugov_get_util(&util, &max);

        raw_spin_lock(&sg_policy->update_lock);

        sg_cpu->util = util;
        sg_cpu->max = max;
        sg_cpu->flags = flags;

        sugov_set_iowait_boost(sg_cpu, time, flags);
        sg_cpu->last_update = time;

        if (sugov_should_update_freq(sg_policy, time)) {
                if (flags & SCHED_CPUFREQ_RT_DL)
                        next_f = sg_policy->policy->cpuinfo.max_freq;
                else
                        next_f = sugov_next_freq_shared(sg_cpu, time);

                sugov_update_commit(sg_policy, time, next_f);
        }

        raw_spin_unlock(&sg_policy->update_lock);
}

static void sugov_work(struct kthread_work *work)
{
        struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work);

        mutex_lock(&sg_policy->work_lock);
        __cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq,
                                CPUFREQ_RELATION_L);
        mutex_unlock(&sg_policy->work_lock);

        sg_policy->work_in_progress = false;
}

static void sugov_irq_work(struct irq_work *irq_work)
{
        struct sugov_policy *sg_policy;

        sg_policy = container_of(irq_work, struct sugov_policy, irq_work);

        /*
         * For RT and deadline tasks, the schedutil governor shoots the
         * frequency to maximum. Special care must be taken to ensure that this
         * kthread doesn't result in the same behavior.
         *
         * This is (mostly) guaranteed by the work_in_progress flag. The flag is
         * updated only at the end of the sugov_work() function and before that
         * the schedutil governor rejects all other frequency scaling requests.
         *
         * There is a very rare case though, where the RT thread yields right
         * after the work_in_progress flag is cleared. The effects of that are
         * neglected for now.
         */
        kthread_queue_work(&sg_policy->worker, &sg_policy->work);
}

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

static struct sugov_tunables *global_tunables;
static DEFINE_MUTEX(global_tunables_lock);

static inline struct sugov_tunables *to_sugov_tunables(struct gov_attr_set *attr_set)
{
        return container_of(attr_set, struct sugov_tunables, attr_set);
}

static ssize_t rate_limit_us_show(struct gov_attr_set *attr_set, char *buf)
{
        struct sugov_tunables *tunables = to_sugov_tunables(attr_set);

        return sprintf(buf, "%u\n", tunables->rate_limit_us);
}

static ssize_t rate_limit_us_store(struct gov_attr_set *attr_set, const char *buf,
                                   size_t count)
{
        struct sugov_tunables *tunables = to_sugov_tunables(attr_set);
        struct sugov_policy *sg_policy;
        unsigned int rate_limit_us;

        if (kstrtouint(buf, 10, &rate_limit_us))
                return -EINVAL;

        tunables->rate_limit_us = rate_limit_us;

        list_for_each_entry(sg_policy, &attr_set->policy_list, tunables_hook)
                sg_policy->freq_update_delay_ns = rate_limit_us * NSEC_PER_USEC;

        return count;
}

static struct governor_attr rate_limit_us = __ATTR_RW(rate_limit_us);

static struct attribute *sugov_attributes[] = {
        &rate_limit_us.attr,
        NULL
};

static struct kobj_type sugov_tunables_ktype = {
        .default_attrs = sugov_attributes,
        .sysfs_ops = &governor_sysfs_ops,
};

/********************** cpufreq governor interface *********************/

static struct cpufreq_governor schedutil_gov;

static struct sugov_policy *sugov_policy_alloc(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy;

        sg_policy = kzalloc(sizeof(*sg_policy), GFP_KERNEL);
        if (!sg_policy)
                return NULL;

        sg_policy->policy = policy;
        raw_spin_lock_init(&sg_policy->update_lock);
        return sg_policy;
}

static void sugov_policy_free(struct sugov_policy *sg_policy)
{
        kfree(sg_policy);
}

static int sugov_kthread_create(struct sugov_policy *sg_policy)
{
        struct task_struct *thread;
        struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO / 2 };
        struct cpufreq_policy *policy = sg_policy->policy;
        int ret;

        /* kthread only required for slow path */
        if (policy->fast_switch_enabled)
                return 0;

        kthread_init_work(&sg_policy->work, sugov_work);
        kthread_init_worker(&sg_policy->worker);
        thread = kthread_create(kthread_worker_fn, &sg_policy->worker,
                                "sugov:%d",
                                cpumask_first(policy->related_cpus));
        if (IS_ERR(thread)) {
                pr_err("failed to create sugov thread: %ld\n", PTR_ERR(thread));
                return PTR_ERR(thread);
        }

        ret = sched_setscheduler_nocheck(thread, SCHED_FIFO, &param);
        if (ret) {
                kthread_stop(thread);
                pr_warn("%s: failed to set SCHED_FIFO\n", __func__);
                return ret;
        }

        sg_policy->thread = thread;
        kthread_bind_mask(thread, policy->related_cpus);
        init_irq_work(&sg_policy->irq_work, sugov_irq_work);
        mutex_init(&sg_policy->work_lock);

        wake_up_process(thread);

        return 0;
}

static void sugov_kthread_stop(struct sugov_policy *sg_policy)
{
        /* kthread only required for slow path */
        if (sg_policy->policy->fast_switch_enabled)
                return;

        kthread_flush_worker(&sg_policy->worker);
        kthread_stop(sg_policy->thread);
        mutex_destroy(&sg_policy->work_lock);
}

static struct sugov_tunables *sugov_tunables_alloc(struct sugov_policy *sg_policy)
{
        struct sugov_tunables *tunables;

        tunables = kzalloc(sizeof(*tunables), GFP_KERNEL);
        if (tunables) {
                gov_attr_set_init(&tunables->attr_set, &sg_policy->tunables_hook);
                if (!have_governor_per_policy())
                        global_tunables = tunables;
        }
        return tunables;
}

static void sugov_tunables_free(struct sugov_tunables *tunables)
{
        if (!have_governor_per_policy())
                global_tunables = NULL;

        kfree(tunables);
}

static int sugov_init(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy;
        struct sugov_tunables *tunables;
        int ret = 0;

        /* State should be equivalent to EXIT */
        if (policy->governor_data)
                return -EBUSY;

        cpufreq_enable_fast_switch(policy);

        sg_policy = sugov_policy_alloc(policy);
        if (!sg_policy) {
                ret = -ENOMEM;
                goto disable_fast_switch;
        }

        ret = sugov_kthread_create(sg_policy);
        if (ret)
                goto free_sg_policy;

        mutex_lock(&global_tunables_lock);

        if (global_tunables) {
                if (WARN_ON(have_governor_per_policy())) {
                        ret = -EINVAL;
                        goto stop_kthread;
                }
                policy->governor_data = sg_policy;
                sg_policy->tunables = global_tunables;

                gov_attr_set_get(&global_tunables->attr_set, &sg_policy->tunables_hook);
                goto out;
        }

        tunables = sugov_tunables_alloc(sg_policy);
        if (!tunables) {
                ret = -ENOMEM;
                goto stop_kthread;
        }

        if (policy->transition_delay_us) {
                tunables->rate_limit_us = policy->transition_delay_us;
        } else {
                unsigned int lat;

                tunables->rate_limit_us = LATENCY_MULTIPLIER;
                lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
                if (lat)
                        tunables->rate_limit_us *= lat;
        }

        policy->governor_data = sg_policy;
        sg_policy->tunables = tunables;

        ret = kobject_init_and_add(&tunables->attr_set.kobj, &sugov_tunables_ktype,
                                   get_governor_parent_kobj(policy), "%s",
                                   schedutil_gov.name);
        if (ret)
                goto fail;

out:
        mutex_unlock(&global_tunables_lock);
        return 0;

fail:
        policy->governor_data = NULL;
        sugov_tunables_free(tunables);

stop_kthread:
        sugov_kthread_stop(sg_policy);

free_sg_policy:
        mutex_unlock(&global_tunables_lock);

        sugov_policy_free(sg_policy);

disable_fast_switch:
        cpufreq_disable_fast_switch(policy);

        pr_err("initialization failed (error %d)\n", ret);
        return ret;
}

static void sugov_exit(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy = policy->governor_data;
        struct sugov_tunables *tunables = sg_policy->tunables;
        unsigned int count;

        mutex_lock(&global_tunables_lock);

        count = gov_attr_set_put(&tunables->attr_set, &sg_policy->tunables_hook);
        policy->governor_data = NULL;
        if (!count)
                sugov_tunables_free(tunables);

        mutex_unlock(&global_tunables_lock);

        sugov_kthread_stop(sg_policy);
        sugov_policy_free(sg_policy);
        cpufreq_disable_fast_switch(policy);
}

static int sugov_start(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy = policy->governor_data;
        unsigned int cpu;

        sg_policy->freq_update_delay_ns = sg_policy->tunables->rate_limit_us * NSEC_PER_USEC;
        sg_policy->last_freq_update_time = 0;
        sg_policy->next_freq = UINT_MAX;
        sg_policy->work_in_progress = false;
        sg_policy->need_freq_update = false;
        sg_policy->cached_raw_freq = 0;

        for_each_cpu(cpu, policy->cpus) {
                struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu);

                memset(sg_cpu, 0, sizeof(*sg_cpu));
                sg_cpu->sg_policy = sg_policy;
                sg_cpu->flags = SCHED_CPUFREQ_RT;
                sg_cpu->iowait_boost_max = policy->cpuinfo.max_freq;
                cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util,
                                             policy_is_shared(policy) ?
                                                        sugov_update_shared :
                                                        sugov_update_single);
        }
        return 0;
}

static void sugov_stop(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy = policy->governor_data;
        unsigned int cpu;

        for_each_cpu(cpu, policy->cpus)
                cpufreq_remove_update_util_hook(cpu);

        synchronize_sched();

        if (!policy->fast_switch_enabled) {
                irq_work_sync(&sg_policy->irq_work);
                kthread_cancel_work_sync(&sg_policy->work);
        }
}

static void sugov_limits(struct cpufreq_policy *policy)
{
        struct sugov_policy *sg_policy = policy->governor_data;

        if (!policy->fast_switch_enabled) {
                mutex_lock(&sg_policy->work_lock);
                cpufreq_policy_apply_limits(policy);
                mutex_unlock(&sg_policy->work_lock);
        }

        sg_policy->need_freq_update = true;
}

static struct cpufreq_governor schedutil_gov = {
        .name = "schedutil",
        .owner = THIS_MODULE,
        .init = sugov_init,
        .exit = sugov_exit,
        .start = sugov_start,
        .stop = sugov_stop,
        .limits = sugov_limits,
};

#ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL
struct cpufreq_governor *cpufreq_default_governor(void)
{
        return &schedutil_gov;
}
#endif

static int __init sugov_register(void)
{
        return cpufreq_register_governor(&schedutil_gov);
}
fs_initcall(sugov_register);