/*
 * itmt.c: Support Intel Turbo Boost Max Technology 3.0
 *
 * (C) Copyright 2016 Intel Corporation
 * Author: Tim Chen <tim.c.chen@linux.intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2
 * of the License.
 *
 * On platforms supporting Intel Turbo Boost Max Technology 3.0, (ITMT),
 * the maximum turbo frequencies of some cores in a CPU package may be
 * higher than for the other cores in the same package.  In that case,
 * better performance can be achieved by making the scheduler prefer
 * to run tasks on the CPUs with higher max turbo frequencies.
 *
 * This file provides functions and data structures for enabling the
 * scheduler to favor scheduling on cores can be boosted to a higher
 * frequency under ITMT.
 */

#include <linux/sched.h>
#include <linux/cpumask.h>
#include <linux/cpuset.h>
#include <linux/mutex.h>
#include <linux/sysctl.h>
#include <linux/nodemask.h>

static DEFINE_MUTEX(itmt_update_mutex);
DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);

/* Boolean to track if system has ITMT capabilities */
static bool __read_mostly sched_itmt_capable;

/*
 * Boolean to control whether we want to move processes to cpu capable
 * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
 * Technology 3.0.
 *
 * It can be set via /proc/sys/kernel/sched_itmt_enabled
 */
unsigned int __read_mostly sysctl_sched_itmt_enabled;

static int sched_itmt_update_handler(struct ctl_table *table, int write,
                                     void __user *buffer, size_t *lenp,
                                     loff_t *ppos)
{
        unsigned int old_sysctl;
        int ret;

        mutex_lock(&itmt_update_mutex);

        if (!sched_itmt_capable) {
                mutex_unlock(&itmt_update_mutex);
                return -EINVAL;
        }

        old_sysctl = sysctl_sched_itmt_enabled;
        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

        if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
                x86_topology_update = true;
                rebuild_sched_domains();
        }

        mutex_unlock(&itmt_update_mutex);

        return ret;
}

static unsigned int zero;
static unsigned int one = 1;
static struct ctl_table itmt_kern_table[] = {
        {
                .procname       = "sched_itmt_enabled",
                .data           = &sysctl_sched_itmt_enabled,
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = sched_itmt_update_handler,
                .extra1         = &zero,
                .extra2         = &one,
        },
        {}
};

static struct ctl_table itmt_root_table[] = {
        {
                .procname       = "kernel",
                .mode           = 0555,
                .child          = itmt_kern_table,
        },
        {}
};

static struct ctl_table_header *itmt_sysctl_header;

/**
 * sched_set_itmt_support() - Indicate platform supports ITMT
 *
 * This function is used by the OS to indicate to scheduler that the platform
 * is capable of supporting the ITMT feature.
 *
 * The current scheme has the pstate driver detects if the system
 * is ITMT capable and call sched_set_itmt_support.
 *
 * This must be done only after sched_set_itmt_core_prio
 * has been called to set the cpus' priorities.
 * It must not be called with cpu hot plug lock
 * held as we need to acquire the lock to rebuild sched domains
 * later.
 *
 * Return: 0 on success
 */
int sched_set_itmt_support(void)
{
        mutex_lock(&itmt_update_mutex);

        if (sched_itmt_capable) {
                mutex_unlock(&itmt_update_mutex);
                return 0;
        }

        itmt_sysctl_header = register_sysctl_table(itmt_root_table);
        if (!itmt_sysctl_header) {
                mutex_unlock(&itmt_update_mutex);
                return -ENOMEM;
        }

        sched_itmt_capable = true;

        sysctl_sched_itmt_enabled = 1;

        x86_topology_update = true;
        rebuild_sched_domains();

        mutex_unlock(&itmt_update_mutex);

        return 0;
}

/**
 * sched_clear_itmt_support() - Revoke platform's support of ITMT
 *
 * This function is used by the OS to indicate that it has
 * revoked the platform's support of ITMT feature.
 *
 * It must not be called with cpu hot plug lock
 * held as we need to acquire the lock to rebuild sched domains
 * later.
 */
void sched_clear_itmt_support(void)
{
        mutex_lock(&itmt_update_mutex);

        if (!sched_itmt_capable) {
                mutex_unlock(&itmt_update_mutex);
                return;
        }
        sched_itmt_capable = false;

        if (itmt_sysctl_header) {
                unregister_sysctl_table(itmt_sysctl_header);
                itmt_sysctl_header = NULL;
        }

        if (sysctl_sched_itmt_enabled) {
                /* disable sched_itmt if we are no longer ITMT capable */
                sysctl_sched_itmt_enabled = 0;
                x86_topology_update = true;
                rebuild_sched_domains();
        }

        mutex_unlock(&itmt_update_mutex);
}

int arch_asym_cpu_priority(int cpu)
{
        return per_cpu(sched_core_priority, cpu);
}

/**
 * sched_set_itmt_core_prio() - Set CPU priority based on ITMT
 * @prio:       Priority of cpu core
 * @core_cpu:   The cpu number associated with the core
 *
 * The pstate driver will find out the max boost frequency
 * and call this function to set a priority proportional
 * to the max boost frequency. CPU with higher boost
 * frequency will receive higher priority.
 *
 * No need to rebuild sched domain after updating
 * the CPU priorities. The sched domains have no
 * dependency on CPU priorities.
 */
void sched_set_itmt_core_prio(int prio, int core_cpu)
{
        int cpu, i = 1;

        for_each_cpu(cpu, topology_sibling_cpumask(core_cpu)) {
                int smt_prio;

                /*
                 * Ensure that the siblings are moved to the end
                 * of the priority chain and only used when
                 * all other high priority cpus are out of capacity.
                 */
                smt_prio = prio * smp_num_siblings / i;
                per_cpu(sched_core_priority, cpu) = smt_prio;
                i++;
        }
}