/*
 *  kernel/sched/cpudl.c
 *
 *  Global CPU deadline management
 *
 *  Author: Juri Lelli <j.lelli@sssup.it>
 *
 *  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.
 */

#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include "cpudeadline.h"

static inline int parent(int i)
{
        return (i - 1) >> 1;
}

static inline int left_child(int i)
{
        return (i << 1) + 1;
}

static inline int right_child(int i)
{
        return (i << 1) + 2;
}

static inline int dl_time_before(u64 a, u64 b)
{
        return (s64)(a - b) < 0;
}

static void cpudl_exchange(struct cpudl *cp, int a, int b)
{
        int cpu_a = cp->elements[a].cpu, cpu_b = cp->elements[b].cpu;

        swap(cp->elements[a].cpu, cp->elements[b].cpu);
        swap(cp->elements[a].dl , cp->elements[b].dl );

        swap(cp->elements[cpu_a].idx, cp->elements[cpu_b].idx);
}

static void cpudl_heapify(struct cpudl *cp, int idx)
{
        int l, r, largest;

        /* adapted from lib/prio_heap.c */
        while(1) {
                l = left_child(idx);
                r = right_child(idx);
                largest = idx;

                if ((l < cp->size) && dl_time_before(cp->elements[idx].dl,
                                                        cp->elements[l].dl))
                        largest = l;
                if ((r < cp->size) && dl_time_before(cp->elements[largest].dl,
                                                        cp->elements[r].dl))
                        largest = r;
                if (largest == idx)
                        break;

                /* Push idx down the heap one level and bump one up */
                cpudl_exchange(cp, largest, idx);
                idx = largest;
        }
}

static void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)
{
        WARN_ON(idx == IDX_INVALID || !cpu_present(idx));

        if (dl_time_before(new_dl, cp->elements[idx].dl)) {
                cp->elements[idx].dl = new_dl;
                cpudl_heapify(cp, idx);
        } else {
                cp->elements[idx].dl = new_dl;
                while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,
                                        cp->elements[idx].dl)) {
                        cpudl_exchange(cp, idx, parent(idx));
                        idx = parent(idx);
                }
        }
}

static inline int cpudl_maximum(struct cpudl *cp)
{
        return cp->elements[0].cpu;
}

/*
 * cpudl_find - find the best (later-dl) CPU in the system
 * @cp: the cpudl max-heap context
 * @p: the task
 * @later_mask: a mask to fill in with the selected CPUs (or NULL)
 *
 * Returns: int - best CPU (heap maximum if suitable)
 */
int cpudl_find(struct cpudl *cp, struct task_struct *p,
               struct cpumask *later_mask)
{
        int best_cpu = -1;
        const struct sched_dl_entity *dl_se = &p->dl;

        if (later_mask && cpumask_and(later_mask, later_mask, cp->free_cpus)) {
                best_cpu = cpumask_any(later_mask);
                goto out;
        } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
                        dl_time_before(dl_se->deadline, cp->elements[0].dl)) {
                best_cpu = cpudl_maximum(cp);
                if (later_mask)
                        cpumask_set_cpu(best_cpu, later_mask);
        }

out:
        WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));

        return best_cpu;
}

/*
 * cpudl_set - update the cpudl max-heap
 * @cp: the cpudl max-heap context
 * @cpu: the target cpu
 * @dl: the new earliest deadline for this cpu
 *
 * Notes: assumes cpu_rq(cpu)->lock is locked
 *
 * Returns: (void)
 */
void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)
{
        int old_idx, new_cpu;
        unsigned long flags;

        WARN_ON(!cpu_present(cpu));

        raw_spin_lock_irqsave(&cp->lock, flags);
        old_idx = cp->elements[cpu].idx;
        if (!is_valid) {
                /* remove item */
                if (old_idx == IDX_INVALID) {
                        /*
                         * Nothing to remove if old_idx was invalid.
                         * This could happen if a rq_offline_dl is
                         * called for a CPU without -dl tasks running.
                         */
                        goto out;
                }
                new_cpu = cp->elements[cp->size - 1].cpu;
                cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
                cp->elements[old_idx].cpu = new_cpu;
                cp->size--;
                cp->elements[new_cpu].idx = old_idx;
                cp->elements[cpu].idx = IDX_INVALID;
                while (old_idx > 0 && dl_time_before(
                                cp->elements[parent(old_idx)].dl,
                                cp->elements[old_idx].dl)) {
                        cpudl_exchange(cp, old_idx, parent(old_idx));
                        old_idx = parent(old_idx);
                }
                cpumask_set_cpu(cpu, cp->free_cpus);
                cpudl_heapify(cp, old_idx);

                goto out;
        }

        if (old_idx == IDX_INVALID) {
                cp->size++;
                cp->elements[cp->size - 1].dl = 0;
                cp->elements[cp->size - 1].cpu = cpu;
                cp->elements[cpu].idx = cp->size - 1;
                cpudl_change_key(cp, cp->size - 1, dl);
                cpumask_clear_cpu(cpu, cp->free_cpus);
        } else {
                cpudl_change_key(cp, old_idx, dl);
        }

out:
        raw_spin_unlock_irqrestore(&cp->lock, flags);
}

/*
 * cpudl_init - initialize the cpudl structure
 * @cp: the cpudl max-heap context
 */
int cpudl_init(struct cpudl *cp)
{
        int i;

        memset(cp, 0, sizeof(*cp));
        raw_spin_lock_init(&cp->lock);
        cp->size = 0;

        cp->elements = kcalloc(nr_cpu_ids,
                               sizeof(struct cpudl_item),
                               GFP_KERNEL);
        if (!cp->elements)
                return -ENOMEM;

        if (!alloc_cpumask_var(&cp->free_cpus, GFP_KERNEL)) {
                kfree(cp->elements);
                return -ENOMEM;
        }

        for_each_possible_cpu(i)
                cp->elements[i].idx = IDX_INVALID;

        cpumask_setall(cp->free_cpus);

        return 0;
}

/*
 * cpudl_cleanup - clean up the cpudl structure
 * @cp: the cpudl max-heap context
 */
void cpudl_cleanup(struct cpudl *cp)
{
        free_cpumask_var(cp->free_cpus);
        kfree(cp->elements);
}