/*
 * intel_powerclamp.c - package c-state idle injection
 *
 * Copyright (c) 2012, Intel Corporation.
 *
 * Authors:
 *     Arjan van de Ven <arjan@linux.intel.com>
 *     Jacob Pan <jacob.jun.pan@linux.intel.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 *
 *
 *      TODO:
 *           1. better handle wakeup from external interrupts, currently a fixed
 *              compensation is added to clamping duration when excessive amount
 *              of wakeups are observed during idle time. the reason is that in
 *              case of external interrupts without need for ack, clamping down
 *              cpu in non-irq context does not reduce irq. for majority of the
 *              cases, clamping down cpu does help reduce irq as well, we should
 *              be able to differenciate the two cases and give a quantitative
 *              solution for the irqs that we can control. perhaps based on
 *              get_cpu_iowait_time_us()
 *
 *           2. synchronization with other hw blocks
 *
 *
 */

#define pr_fmt(fmt)     KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/cpu.h>
#include <linux/thermal.h>
#include <linux/slab.h>
#include <linux/tick.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/sched/rt.h>

#include <asm/nmi.h>
#include <asm/msr.h>
#include <asm/mwait.h>
#include <asm/cpu_device_id.h>
#include <asm/idle.h>
#include <asm/hardirq.h>

#define MAX_TARGET_RATIO (50U)
/* For each undisturbed clamping period (no extra wake ups during idle time),
 * we increment the confidence counter for the given target ratio.
 * CONFIDENCE_OK defines the level where runtime calibration results are
 * valid.
 */
#define CONFIDENCE_OK (3)
/* Default idle injection duration, driver adjust sleep time to meet target
 * idle ratio. Similar to frequency modulation.
 */
#define DEFAULT_DURATION_JIFFIES (6)

static unsigned int target_mwait;
static struct dentry *debug_dir;

/* user selected target */
static unsigned int set_target_ratio;
static unsigned int current_ratio;
static bool should_skip;
static bool reduce_irq;
static atomic_t idle_wakeup_counter;
static unsigned int control_cpu; /* The cpu assigned to collect stat and update
                                  * control parameters. default to BSP but BSP
                                  * can be offlined.
                                  */
static bool clamping;


static struct task_struct * __percpu *powerclamp_thread;
static struct thermal_cooling_device *cooling_dev;
static unsigned long *cpu_clamping_mask;  /* bit map for tracking per cpu
                                           * clamping thread
                                           */

static unsigned int duration;
static unsigned int pkg_cstate_ratio_cur;
static unsigned int window_size;

static int duration_set(const char *arg, const struct kernel_param *kp)
{
        int ret = 0;
        unsigned long new_duration;

        ret = kstrtoul(arg, 10, &new_duration);
        if (ret)
                goto exit;
        if (new_duration > 25 || new_duration < 6) {
                pr_err("Out of recommended range %lu, between 6-25ms\n",
                        new_duration);
                ret = -EINVAL;
        }

        duration = clamp(new_duration, 6ul, 25ul);
        smp_mb();

exit:

        return ret;
}

static const struct kernel_param_ops duration_ops = {
        .set = duration_set,
        .get = param_get_int,
};


module_param_cb(duration, &duration_ops, &duration, 0644);
MODULE_PARM_DESC(duration, "forced idle time for each attempt in msec.");

struct powerclamp_calibration_data {
        unsigned long confidence;  /* used for calibration, basically a counter
                                    * gets incremented each time a clamping
                                    * period is completed without extra wakeups
                                    * once that counter is reached given level,
                                    * compensation is deemed usable.
                                    */
        unsigned long steady_comp; /* steady state compensation used when
                                    * no extra wakeups occurred.
                                    */
        unsigned long dynamic_comp; /* compensate excessive wakeup from idle
                                     * mostly from external interrupts.
                                     */
};

static struct powerclamp_calibration_data cal_data[MAX_TARGET_RATIO];

static int window_size_set(const char *arg, const struct kernel_param *kp)
{
        int ret = 0;
        unsigned long new_window_size;

        ret = kstrtoul(arg, 10, &new_window_size);
        if (ret)
                goto exit_win;
        if (new_window_size > 10 || new_window_size < 2) {
                pr_err("Out of recommended window size %lu, between 2-10\n",
                        new_window_size);
                ret = -EINVAL;
        }

        window_size = clamp(new_window_size, 2ul, 10ul);
        smp_mb();

exit_win:

        return ret;
}

static const struct kernel_param_ops window_size_ops = {
        .set = window_size_set,
        .get = param_get_int,
};

module_param_cb(window_size, &window_size_ops, &window_size, 0644);
MODULE_PARM_DESC(window_size, "sliding window in number of clamping cycles\n"
        "\tpowerclamp controls idle ratio within this window. larger\n"
        "\twindow size results in slower response time but more smooth\n"
        "\tclamping results. default to 2.");

static void find_target_mwait(void)
{
        unsigned int eax, ebx, ecx, edx;
        unsigned int highest_cstate = 0;
        unsigned int highest_subcstate = 0;
        int i;

        if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
                return;

        cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);

        if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
            !(ecx & CPUID5_ECX_INTERRUPT_BREAK))
                return;

        edx >>= MWAIT_SUBSTATE_SIZE;
        for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
                if (edx & MWAIT_SUBSTATE_MASK) {
                        highest_cstate = i;
                        highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
                }
        }
        target_mwait = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
                (highest_subcstate - 1);

}

struct pkg_cstate_info {
        bool skip;
        int msr_index;
        int cstate_id;
};

#define PKG_CSTATE_INIT(id) {                           \
                .msr_index = MSR_PKG_C##id##_RESIDENCY, \
                .cstate_id = id                         \
                        }

static struct pkg_cstate_info pkg_cstates[] = {
        PKG_CSTATE_INIT(2),
        PKG_CSTATE_INIT(3),
        PKG_CSTATE_INIT(6),
        PKG_CSTATE_INIT(7),
        PKG_CSTATE_INIT(8),
        PKG_CSTATE_INIT(9),
        PKG_CSTATE_INIT(10),
        {NULL},
};

static bool has_pkg_state_counter(void)
{
        u64 val;
        struct pkg_cstate_info *info = pkg_cstates;

        /* check if any one of the counter msrs exists */
        while (info->msr_index) {
                if (!rdmsrl_safe(info->msr_index, &val))
                        return true;
                info++;
        }

        return false;
}

static u64 pkg_state_counter(void)
{
        u64 val;
        u64 count = 0;
        struct pkg_cstate_info *info = pkg_cstates;

        while (info->msr_index) {
                if (!info->skip) {
                        if (!rdmsrl_safe(info->msr_index, &val))
                                count += val;
                        else
                                info->skip = true;
                }
                info++;
        }

        return count;
}

static void noop_timer(unsigned long foo)
{
        /* empty... just the fact that we get the interrupt wakes us up */
}

static unsigned int get_compensation(int ratio)
{
        unsigned int comp = 0;

        /* we only use compensation if all adjacent ones are good */
        if (ratio == 1 &&
                cal_data[ratio].confidence >= CONFIDENCE_OK &&
                cal_data[ratio + 1].confidence >= CONFIDENCE_OK &&
                cal_data[ratio + 2].confidence >= CONFIDENCE_OK) {
                comp = (cal_data[ratio].steady_comp +
                        cal_data[ratio + 1].steady_comp +
                        cal_data[ratio + 2].steady_comp) / 3;
        } else if (ratio == MAX_TARGET_RATIO - 1 &&
                cal_data[ratio].confidence >= CONFIDENCE_OK &&
                cal_data[ratio - 1].confidence >= CONFIDENCE_OK &&
                cal_data[ratio - 2].confidence >= CONFIDENCE_OK) {
                comp = (cal_data[ratio].steady_comp +
                        cal_data[ratio - 1].steady_comp +
                        cal_data[ratio - 2].steady_comp) / 3;
        } else if (cal_data[ratio].confidence >= CONFIDENCE_OK &&
                cal_data[ratio - 1].confidence >= CONFIDENCE_OK &&
                cal_data[ratio + 1].confidence >= CONFIDENCE_OK) {
                comp = (cal_data[ratio].steady_comp +
                        cal_data[ratio - 1].steady_comp +
                        cal_data[ratio + 1].steady_comp) / 3;
        }

        /* REVISIT: simple penalty of double idle injection */
        if (reduce_irq)
                comp = ratio;
        /* do not exceed limit */
        if (comp + ratio >= MAX_TARGET_RATIO)
                comp = MAX_TARGET_RATIO - ratio - 1;

        return comp;
}

static void adjust_compensation(int target_ratio, unsigned int win)
{
        int delta;
        struct powerclamp_calibration_data *d = &cal_data[target_ratio];

        /*
         * adjust compensations if confidence level has not been reached or
         * there are too many wakeups during the last idle injection period, we
         * cannot trust the data for compensation.
         */
        if (d->confidence >= CONFIDENCE_OK ||
                atomic_read(&idle_wakeup_counter) >
                win * num_online_cpus())
                return;

        delta = set_target_ratio - current_ratio;
        /* filter out bad data */
        if (delta >= 0 && delta <= (1+target_ratio/10)) {
                if (d->steady_comp)
                        d->steady_comp =
                                roundup(delta+d->steady_comp, 2)/2;
                else
                        d->steady_comp = delta;
                d->confidence++;
        }
}

static bool powerclamp_adjust_controls(unsigned int target_ratio,
                                unsigned int guard, unsigned int win)
{
        static u64 msr_last, tsc_last;
        u64 msr_now, tsc_now;
        u64 val64;

        /* check result for the last window */
        msr_now = pkg_state_counter();
        tsc_now = rdtsc();

        /* calculate pkg cstate vs tsc ratio */
        if (!msr_last || !tsc_last)
                current_ratio = 1;
        else if (tsc_now-tsc_last) {
                val64 = 100*(msr_now-msr_last);
                do_div(val64, (tsc_now-tsc_last));
                current_ratio = val64;
        }

        /* update record */
        msr_last = msr_now;
        tsc_last = tsc_now;

        adjust_compensation(target_ratio, win);
        /*
         * too many external interrupts, set flag such
         * that we can take measure later.
         */
        reduce_irq = atomic_read(&idle_wakeup_counter) >=
                2 * win * num_online_cpus();

        atomic_set(&idle_wakeup_counter, 0);
        /* if we are above target+guard, skip */
        return set_target_ratio + guard <= current_ratio;
}

static int clamp_thread(void *arg)
{
        int cpunr = (unsigned long)arg;
        DEFINE_TIMER(wakeup_timer, noop_timer, 0, 0);
        static const struct sched_param param = {
                .sched_priority = MAX_USER_RT_PRIO/2,
        };
        unsigned int count = 0;
        unsigned int target_ratio;

        set_bit(cpunr, cpu_clamping_mask);
        set_freezable();
        init_timer_on_stack(&wakeup_timer);
        sched_setscheduler(current, SCHED_FIFO, &param);

        while (true == clamping && !kthread_should_stop() &&
                cpu_online(cpunr)) {
                int sleeptime;
                unsigned long target_jiffies;
                unsigned int guard;
                unsigned int compensated_ratio;
                int interval; /* jiffies to sleep for each attempt */
                unsigned int duration_jiffies = msecs_to_jiffies(duration);
                unsigned int window_size_now;

                try_to_freeze();
                /*
                 * make sure user selected ratio does not take effect until
                 * the next round. adjust target_ratio if user has changed
                 * target such that we can converge quickly.
                 */
                target_ratio = set_target_ratio;
                guard = 1 + target_ratio/20;
                window_size_now = window_size;
                count++;

                /*
                 * systems may have different ability to enter package level
                 * c-states, thus we need to compensate the injected idle ratio
                 * to achieve the actual target reported by the HW.
                 */
                compensated_ratio = target_ratio +
                        get_compensation(target_ratio);
                if (compensated_ratio <= 0)
                        compensated_ratio = 1;
                interval = duration_jiffies * 100 / compensated_ratio;

                /* align idle time */
                target_jiffies = roundup(jiffies, interval);
                sleeptime = target_jiffies - jiffies;
                if (sleeptime <= 0)
                        sleeptime = 1;
                schedule_timeout_interruptible(sleeptime);
                /*
                 * only elected controlling cpu can collect stats and update
                 * control parameters.
                 */
                if (cpunr == control_cpu && !(count%window_size_now)) {
                        should_skip =
                                powerclamp_adjust_controls(target_ratio,
                                                        guard, window_size_now);
                        smp_mb();
                }

                if (should_skip)
                        continue;

                target_jiffies = jiffies + duration_jiffies;
                mod_timer(&wakeup_timer, target_jiffies);
                if (unlikely(local_softirq_pending()))
                        continue;
                /*
                 * stop tick sched during idle time, interrupts are still
                 * allowed. thus jiffies are updated properly.
                 */
                preempt_disable();
                /* mwait until target jiffies is reached */
                while (time_before(jiffies, target_jiffies)) {
                        unsigned long ecx = 1;
                        unsigned long eax = target_mwait;

                        /*
                         * REVISIT: may call enter_idle() to notify drivers who
                         * can save power during cpu idle. same for exit_idle()
                         */
                        local_touch_nmi();
                        stop_critical_timings();
                        mwait_idle_with_hints(eax, ecx);
                        start_critical_timings();
                        atomic_inc(&idle_wakeup_counter);
                }
                preempt_enable();
        }
        del_timer_sync(&wakeup_timer);
        clear_bit(cpunr, cpu_clamping_mask);

        return 0;
}

/*
 * 1 HZ polling while clamping is active, useful for userspace
 * to monitor actual idle ratio.
 */
static void poll_pkg_cstate(struct work_struct *dummy);
static DECLARE_DELAYED_WORK(poll_pkg_cstate_work, poll_pkg_cstate);
static void poll_pkg_cstate(struct work_struct *dummy)
{
        static u64 msr_last;
        static u64 tsc_last;
        static unsigned long jiffies_last;

        u64 msr_now;
        unsigned long jiffies_now;
        u64 tsc_now;
        u64 val64;

        msr_now = pkg_state_counter();
        tsc_now = rdtsc();
        jiffies_now = jiffies;

        /* calculate pkg cstate vs tsc ratio */
        if (!msr_last || !tsc_last)
                pkg_cstate_ratio_cur = 1;
        else {
                if (tsc_now - tsc_last) {
                        val64 = 100 * (msr_now - msr_last);
                        do_div(val64, (tsc_now - tsc_last));
                        pkg_cstate_ratio_cur = val64;
                }
        }

        /* update record */
        msr_last = msr_now;
        jiffies_last = jiffies_now;
        tsc_last = tsc_now;

        if (true == clamping)
                schedule_delayed_work(&poll_pkg_cstate_work, HZ);
}

static int start_power_clamp(void)
{
        unsigned long cpu;
        struct task_struct *thread;

        set_target_ratio = clamp(set_target_ratio, 0U, MAX_TARGET_RATIO - 1);
        /* prevent cpu hotplug */
        get_online_cpus();

        /* prefer BSP */
        control_cpu = 0;
        if (!cpu_online(control_cpu))
                control_cpu = smp_processor_id();

        clamping = true;
        schedule_delayed_work(&poll_pkg_cstate_work, 0);

        /* start one thread per online cpu */
        for_each_online_cpu(cpu) {
                struct task_struct **p =
                        per_cpu_ptr(powerclamp_thread, cpu);

                thread = kthread_create_on_node(clamp_thread,
                                                (void *) cpu,
                                                cpu_to_node(cpu),
                                                "kidle_inject/%ld", cpu);
                /* bind to cpu here */
                if (likely(!IS_ERR(thread))) {
                        kthread_bind(thread, cpu);
                        wake_up_process(thread);
                        *p = thread;
                }

        }
        put_online_cpus();

        return 0;
}

static void end_power_clamp(void)
{
        int i;
        struct task_struct *thread;

        clamping = false;
        /*
         * make clamping visible to other cpus and give per cpu clamping threads
         * sometime to exit, or gets killed later.
         */
        smp_mb();
        msleep(20);
        if (bitmap_weight(cpu_clamping_mask, num_possible_cpus())) {
                for_each_set_bit(i, cpu_clamping_mask, num_possible_cpus()) {
                        pr_debug("clamping thread for cpu %d alive, kill\n", i);
                        thread = *per_cpu_ptr(powerclamp_thread, i);
                        kthread_stop(thread);
                }
        }
}

static int powerclamp_cpu_callback(struct notifier_block *nfb,
                                unsigned long action, void *hcpu)
{
        unsigned long cpu = (unsigned long)hcpu;
        struct task_struct *thread;
        struct task_struct **percpu_thread =
                per_cpu_ptr(powerclamp_thread, cpu);

        if (false == clamping)
                goto exit_ok;

        switch (action) {
        case CPU_ONLINE:
                thread = kthread_create_on_node(clamp_thread,
                                                (void *) cpu,
                                                cpu_to_node(cpu),
                                                "kidle_inject/%lu", cpu);
                if (likely(!IS_ERR(thread))) {
                        kthread_bind(thread, cpu);
                        wake_up_process(thread);
                        *percpu_thread = thread;
                }
                /* prefer BSP as controlling CPU */
                if (cpu == 0) {
                        control_cpu = 0;
                        smp_mb();
                }
                break;
        case CPU_DEAD:
                if (test_bit(cpu, cpu_clamping_mask)) {
                        pr_err("cpu %lu dead but powerclamping thread is not\n",
                                cpu);
                        kthread_stop(*percpu_thread);
                }
                if (cpu == control_cpu) {
                        control_cpu = smp_processor_id();
                        smp_mb();
                }
        }

exit_ok:
        return NOTIFY_OK;
}

static struct notifier_block powerclamp_cpu_notifier = {
        .notifier_call = powerclamp_cpu_callback,
};

static int powerclamp_get_max_state(struct thermal_cooling_device *cdev,
                                 unsigned long *state)
{
        *state = MAX_TARGET_RATIO;

        return 0;
}

static int powerclamp_get_cur_state(struct thermal_cooling_device *cdev,
                                 unsigned long *state)
{
        if (true == clamping)
                *state = pkg_cstate_ratio_cur;
        else
                /* to save power, do not poll idle ratio while not clamping */
                *state = -1; /* indicates invalid state */

        return 0;
}

static int powerclamp_set_cur_state(struct thermal_cooling_device *cdev,
                                 unsigned long new_target_ratio)
{
        int ret = 0;

        new_target_ratio = clamp(new_target_ratio, 0UL,
                                (unsigned long) (MAX_TARGET_RATIO-1));
        if (set_target_ratio == 0 && new_target_ratio > 0) {
                pr_info("Start idle injection to reduce power\n");
                set_target_ratio = new_target_ratio;
                ret = start_power_clamp();
                goto exit_set;
        } else  if (set_target_ratio > 0 && new_target_ratio == 0) {
                pr_info("Stop forced idle injection\n");
                end_power_clamp();
                set_target_ratio = 0;
        } else  /* adjust currently running */ {
                set_target_ratio = new_target_ratio;
                /* make new set_target_ratio visible to other cpus */
                smp_mb();
        }

exit_set:
        return ret;
}

/* bind to generic thermal layer as cooling device*/
static struct thermal_cooling_device_ops powerclamp_cooling_ops = {
        .get_max_state = powerclamp_get_max_state,
        .get_cur_state = powerclamp_get_cur_state,
        .set_cur_state = powerclamp_set_cur_state,
};

static const struct x86_cpu_id __initconst intel_powerclamp_ids[] = {
        { X86_VENDOR_INTEL, X86_FAMILY_ANY, X86_MODEL_ANY, X86_FEATURE_MWAIT },
        {}
};
MODULE_DEVICE_TABLE(x86cpu, intel_powerclamp_ids);

static int __init powerclamp_probe(void)
{

        if (!x86_match_cpu(intel_powerclamp_ids)) {
                pr_err("CPU does not support MWAIT");
                return -ENODEV;
        }

        /* The goal for idle time alignment is to achieve package cstate. */
        if (!has_pkg_state_counter()) {
                pr_info("No package C-state available");
                return -ENODEV;
        }

        /* find the deepest mwait value */
        find_target_mwait();

        return 0;
}

static int powerclamp_debug_show(struct seq_file *m, void *unused)
{
        int i = 0;

        seq_printf(m, "controlling cpu: %d\n", control_cpu);
        seq_printf(m, "pct confidence steady dynamic (compensation)\n");
        for (i = 0; i < MAX_TARGET_RATIO; i++) {
                seq_printf(m, "%d\t%lu\t%lu\t%lu\n",
                        i,
                        cal_data[i].confidence,
                        cal_data[i].steady_comp,
                        cal_data[i].dynamic_comp);
        }

        return 0;
}

static int powerclamp_debug_open(struct inode *inode,
                        struct file *file)
{
        return single_open(file, powerclamp_debug_show, inode->i_private);
}

static const struct file_operations powerclamp_debug_fops = {
        .open           = powerclamp_debug_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
        .owner          = THIS_MODULE,
};

static inline void powerclamp_create_debug_files(void)
{
        debug_dir = debugfs_create_dir("intel_powerclamp", NULL);
        if (!debug_dir)
                return;

        if (!debugfs_create_file("powerclamp_calib", S_IRUGO, debug_dir,
                                        cal_data, &powerclamp_debug_fops))
                goto file_error;

        return;

file_error:
        debugfs_remove_recursive(debug_dir);
}

static int __init powerclamp_init(void)
{
        int retval;
        int bitmap_size;

        bitmap_size = BITS_TO_LONGS(num_possible_cpus()) * sizeof(long);
        cpu_clamping_mask = kzalloc(bitmap_size, GFP_KERNEL);
        if (!cpu_clamping_mask)
                return -ENOMEM;

        /* probe cpu features and ids here */
        retval = powerclamp_probe();
        if (retval)
                goto exit_free;

        /* set default limit, maybe adjusted during runtime based on feedback */
        window_size = 2;
        register_hotcpu_notifier(&powerclamp_cpu_notifier);

        powerclamp_thread = alloc_percpu(struct task_struct *);
        if (!powerclamp_thread) {
                retval = -ENOMEM;
                goto exit_unregister;
        }

        cooling_dev = thermal_cooling_device_register("intel_powerclamp", NULL,
                                                &powerclamp_cooling_ops);
        if (IS_ERR(cooling_dev)) {
                retval = -ENODEV;
                goto exit_free_thread;
        }

        if (!duration)
                duration = jiffies_to_msecs(DEFAULT_DURATION_JIFFIES);

        powerclamp_create_debug_files();

        return 0;

exit_free_thread:
        free_percpu(powerclamp_thread);
exit_unregister:
        unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
exit_free:
        kfree(cpu_clamping_mask);
        return retval;
}
module_init(powerclamp_init);

static void __exit powerclamp_exit(void)
{
        unregister_hotcpu_notifier(&powerclamp_cpu_notifier);
        end_power_clamp();
        free_percpu(powerclamp_thread);
        thermal_cooling_device_unregister(cooling_dev);
        kfree(cpu_clamping_mask);

        cancel_delayed_work_sync(&poll_pkg_cstate_work);
        debugfs_remove_recursive(debug_dir);
}
module_exit(powerclamp_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@linux.intel.com>");
MODULE_DESCRIPTION("Package Level C-state Idle Injection for Intel CPUs");