License cleanup: add SPDX GPL-2.0 license identifier to files with no license

[mirror_ubuntu-kernels.git] / kernel / sched / topology.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Scheduler topology setup/handling methods
 */
#include <linux/sched.h>
#include <linux/mutex.h>

#include "sched.h"

DEFINE_MUTEX(sched_domains_mutex);

/* Protected by sched_domains_mutex: */
cpumask_var_t sched_domains_tmpmask;
cpumask_var_t sched_domains_tmpmask2;

#ifdef CONFIG_SCHED_DEBUG

static int __init sched_debug_setup(char *str)
{
        sched_debug_enabled = true;

        return 0;
}
early_param("sched_debug", sched_debug_setup);

static inline bool sched_debug(void)
{
        return sched_debug_enabled;
}

static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
                                  struct cpumask *groupmask)
{
        struct sched_group *group = sd->groups;

        cpumask_clear(groupmask);

        printk(KERN_DEBUG "%*s domain-%d: ", level, "", level);

        if (!(sd->flags & SD_LOAD_BALANCE)) {
                printk("does not load-balance\n");
                if (sd->parent)
                        printk(KERN_ERR "ERROR: !SD_LOAD_BALANCE domain"
                                        " has parent");
                return -1;
        }

        printk(KERN_CONT "span=%*pbl level=%s\n",
               cpumask_pr_args(sched_domain_span(sd)), sd->name);

        if (!cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                printk(KERN_ERR "ERROR: domain->span does not contain "
                                "CPU%d\n", cpu);
        }
        if (!cpumask_test_cpu(cpu, sched_group_span(group))) {
                printk(KERN_ERR "ERROR: domain->groups does not contain"
                                " CPU%d\n", cpu);
        }

        printk(KERN_DEBUG "%*s groups:", level + 1, "");
        do {
                if (!group) {
                        printk("\n");
                        printk(KERN_ERR "ERROR: group is NULL\n");
                        break;
                }

                if (!cpumask_weight(sched_group_span(group))) {
                        printk(KERN_CONT "\n");
                        printk(KERN_ERR "ERROR: empty group\n");
                        break;
                }

                if (!(sd->flags & SD_OVERLAP) &&
                    cpumask_intersects(groupmask, sched_group_span(group))) {
                        printk(KERN_CONT "\n");
                        printk(KERN_ERR "ERROR: repeated CPUs\n");
                        break;
                }

                cpumask_or(groupmask, groupmask, sched_group_span(group));

                printk(KERN_CONT " %d:{ span=%*pbl",
                                group->sgc->id,
                                cpumask_pr_args(sched_group_span(group)));

                if ((sd->flags & SD_OVERLAP) &&
                    !cpumask_equal(group_balance_mask(group), sched_group_span(group))) {
                        printk(KERN_CONT " mask=%*pbl",
                                cpumask_pr_args(group_balance_mask(group)));
                }

                if (group->sgc->capacity != SCHED_CAPACITY_SCALE)
                        printk(KERN_CONT " cap=%lu", group->sgc->capacity);

                if (group == sd->groups && sd->child &&
                    !cpumask_equal(sched_domain_span(sd->child),
                                   sched_group_span(group))) {
                        printk(KERN_ERR "ERROR: domain->groups does not match domain->child\n");
                }

                printk(KERN_CONT " }");

                group = group->next;

                if (group != sd->groups)
                        printk(KERN_CONT ",");

        } while (group != sd->groups);
        printk(KERN_CONT "\n");

        if (!cpumask_equal(sched_domain_span(sd), groupmask))
                printk(KERN_ERR "ERROR: groups don't span domain->span\n");

        if (sd->parent &&
            !cpumask_subset(groupmask, sched_domain_span(sd->parent)))
                printk(KERN_ERR "ERROR: parent span is not a superset "
                        "of domain->span\n");
        return 0;
}

static void sched_domain_debug(struct sched_domain *sd, int cpu)
{
        int level = 0;

        if (!sched_debug_enabled)
                return;

        if (!sd) {
                printk(KERN_DEBUG "CPU%d attaching NULL sched-domain.\n", cpu);
                return;
        }

        printk(KERN_DEBUG "CPU%d attaching sched-domain(s):\n", cpu);

        for (;;) {
                if (sched_domain_debug_one(sd, cpu, level, sched_domains_tmpmask))
                        break;
                level++;
                sd = sd->parent;
                if (!sd)
                        break;
        }
}
#else /* !CONFIG_SCHED_DEBUG */

# define sched_debug_enabled 0
# define sched_domain_debug(sd, cpu) do { } while (0)
static inline bool sched_debug(void)
{
        return false;
}
#endif /* CONFIG_SCHED_DEBUG */

static int sd_degenerate(struct sched_domain *sd)
{
        if (cpumask_weight(sched_domain_span(sd)) == 1)
                return 1;

        /* Following flags need at least 2 groups */
        if (sd->flags & (SD_LOAD_BALANCE |
                         SD_BALANCE_NEWIDLE |
                         SD_BALANCE_FORK |
                         SD_BALANCE_EXEC |
                         SD_SHARE_CPUCAPACITY |
                         SD_ASYM_CPUCAPACITY |
                         SD_SHARE_PKG_RESOURCES |
                         SD_SHARE_POWERDOMAIN)) {
                if (sd->groups != sd->groups->next)
                        return 0;
        }

        /* Following flags don't use groups */
        if (sd->flags & (SD_WAKE_AFFINE))
                return 0;

        return 1;
}

static int
sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
{
        unsigned long cflags = sd->flags, pflags = parent->flags;

        if (sd_degenerate(parent))
                return 1;

        if (!cpumask_equal(sched_domain_span(sd), sched_domain_span(parent)))
                return 0;

        /* Flags needing groups don't count if only 1 group in parent */
        if (parent->groups == parent->groups->next) {
                pflags &= ~(SD_LOAD_BALANCE |
                                SD_BALANCE_NEWIDLE |
                                SD_BALANCE_FORK |
                                SD_BALANCE_EXEC |
                                SD_ASYM_CPUCAPACITY |
                                SD_SHARE_CPUCAPACITY |
                                SD_SHARE_PKG_RESOURCES |
                                SD_PREFER_SIBLING |
                                SD_SHARE_POWERDOMAIN);
                if (nr_node_ids == 1)
                        pflags &= ~SD_SERIALIZE;
        }
        if (~cflags & pflags)
                return 0;

        return 1;
}

static void free_rootdomain(struct rcu_head *rcu)
{
        struct root_domain *rd = container_of(rcu, struct root_domain, rcu);

        cpupri_cleanup(&rd->cpupri);
        cpudl_cleanup(&rd->cpudl);
        free_cpumask_var(rd->dlo_mask);
        free_cpumask_var(rd->rto_mask);
        free_cpumask_var(rd->online);
        free_cpumask_var(rd->span);
        kfree(rd);
}

void rq_attach_root(struct rq *rq, struct root_domain *rd)
{
        struct root_domain *old_rd = NULL;
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);

        if (rq->rd) {
                old_rd = rq->rd;

                if (cpumask_test_cpu(rq->cpu, old_rd->online))
                        set_rq_offline(rq);

                cpumask_clear_cpu(rq->cpu, old_rd->span);

                /*
                 * If we dont want to free the old_rd yet then
                 * set old_rd to NULL to skip the freeing later
                 * in this function:
                 */
                if (!atomic_dec_and_test(&old_rd->refcount))
                        old_rd = NULL;
        }

        atomic_inc(&rd->refcount);
        rq->rd = rd;

        cpumask_set_cpu(rq->cpu, rd->span);
        if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
                set_rq_online(rq);

        raw_spin_unlock_irqrestore(&rq->lock, flags);

        if (old_rd)
                call_rcu_sched(&old_rd->rcu, free_rootdomain);
}

static int init_rootdomain(struct root_domain *rd)
{
        if (!zalloc_cpumask_var(&rd->span, GFP_KERNEL))
                goto out;
        if (!zalloc_cpumask_var(&rd->online, GFP_KERNEL))
                goto free_span;
        if (!zalloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
                goto free_online;
        if (!zalloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
                goto free_dlo_mask;

        init_dl_bw(&rd->dl_bw);
        if (cpudl_init(&rd->cpudl) != 0)
                goto free_rto_mask;

        if (cpupri_init(&rd->cpupri) != 0)
                goto free_cpudl;
        return 0;

free_cpudl:
        cpudl_cleanup(&rd->cpudl);
free_rto_mask:
        free_cpumask_var(rd->rto_mask);
free_dlo_mask:
        free_cpumask_var(rd->dlo_mask);
free_online:
        free_cpumask_var(rd->online);
free_span:
        free_cpumask_var(rd->span);
out:
        return -ENOMEM;
}

/*
 * By default the system creates a single root-domain with all CPUs as
 * members (mimicking the global state we have today).
 */
struct root_domain def_root_domain;

void init_defrootdomain(void)
{
        init_rootdomain(&def_root_domain);

        atomic_set(&def_root_domain.refcount, 1);
}

static struct root_domain *alloc_rootdomain(void)
{
        struct root_domain *rd;

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

        if (init_rootdomain(rd) != 0) {
                kfree(rd);
                return NULL;
        }

        return rd;
}

static void free_sched_groups(struct sched_group *sg, int free_sgc)
{
        struct sched_group *tmp, *first;

        if (!sg)
                return;

        first = sg;
        do {
                tmp = sg->next;

                if (free_sgc && atomic_dec_and_test(&sg->sgc->ref))
                        kfree(sg->sgc);

                if (atomic_dec_and_test(&sg->ref))
                        kfree(sg);
                sg = tmp;
        } while (sg != first);
}

static void destroy_sched_domain(struct sched_domain *sd)
{
        /*
         * A normal sched domain may have multiple group references, an
         * overlapping domain, having private groups, only one.  Iterate,
         * dropping group/capacity references, freeing where none remain.
         */
        free_sched_groups(sd->groups, 1);

        if (sd->shared && atomic_dec_and_test(&sd->shared->ref))
                kfree(sd->shared);
        kfree(sd);
}

static void destroy_sched_domains_rcu(struct rcu_head *rcu)
{
        struct sched_domain *sd = container_of(rcu, struct sched_domain, rcu);

        while (sd) {
                struct sched_domain *parent = sd->parent;
                destroy_sched_domain(sd);
                sd = parent;
        }
}

static void destroy_sched_domains(struct sched_domain *sd)
{
        if (sd)
                call_rcu(&sd->rcu, destroy_sched_domains_rcu);
}

/*
 * Keep a special pointer to the highest sched_domain that has
 * SD_SHARE_PKG_RESOURCE set (Last Level Cache Domain) for this
 * allows us to avoid some pointer chasing select_idle_sibling().
 *
 * Also keep a unique ID per domain (we use the first CPU number in
 * the cpumask of the domain), this allows us to quickly tell if
 * two CPUs are in the same cache domain, see cpus_share_cache().
 */
DEFINE_PER_CPU(struct sched_domain *, sd_llc);
DEFINE_PER_CPU(int, sd_llc_size);
DEFINE_PER_CPU(int, sd_llc_id);
DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
DEFINE_PER_CPU(struct sched_domain *, sd_asym);

static void update_top_cache_domain(int cpu)
{
        struct sched_domain_shared *sds = NULL;
        struct sched_domain *sd;
        int id = cpu;
        int size = 1;

        sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES);
        if (sd) {
                id = cpumask_first(sched_domain_span(sd));
                size = cpumask_weight(sched_domain_span(sd));
                sds = sd->shared;
        }

        rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
        per_cpu(sd_llc_size, cpu) = size;
        per_cpu(sd_llc_id, cpu) = id;
        rcu_assign_pointer(per_cpu(sd_llc_shared, cpu), sds);

        sd = lowest_flag_domain(cpu, SD_NUMA);
        rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);

        sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
        rcu_assign_pointer(per_cpu(sd_asym, cpu), sd);
}

/*
 * Attach the domain 'sd' to 'cpu' as its base domain. Callers must
 * hold the hotplug lock.
 */
static void
cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct sched_domain *tmp;

        /* Remove the sched domains which do not contribute to scheduling. */
        for (tmp = sd; tmp; ) {
                struct sched_domain *parent = tmp->parent;
                if (!parent)
                        break;

                if (sd_parent_degenerate(tmp, parent)) {
                        tmp->parent = parent->parent;
                        if (parent->parent)
                                parent->parent->child = tmp;
                        /*
                         * Transfer SD_PREFER_SIBLING down in case of a
                         * degenerate parent; the spans match for this
                         * so the property transfers.
                         */
                        if (parent->flags & SD_PREFER_SIBLING)
                                tmp->flags |= SD_PREFER_SIBLING;
                        destroy_sched_domain(parent);
                } else
                        tmp = tmp->parent;
        }

        if (sd && sd_degenerate(sd)) {
                tmp = sd;
                sd = sd->parent;
                destroy_sched_domain(tmp);
                if (sd)
                        sd->child = NULL;
        }

        sched_domain_debug(sd, cpu);

        rq_attach_root(rq, rd);
        tmp = rq->sd;
        rcu_assign_pointer(rq->sd, sd);
        dirty_sched_domain_sysctl(cpu);
        destroy_sched_domains(tmp);

        update_top_cache_domain(cpu);
}

/* Setup the mask of CPUs configured for isolated domains */
static int __init isolated_cpu_setup(char *str)
{
        int ret;

        alloc_bootmem_cpumask_var(&cpu_isolated_map);
        ret = cpulist_parse(str, cpu_isolated_map);
        if (ret) {
                pr_err("sched: Error, all isolcpus= values must be between 0 and %u\n", nr_cpu_ids);
                return 0;
        }
        return 1;
}
__setup("isolcpus=", isolated_cpu_setup);

struct s_data {
        struct sched_domain ** __percpu sd;
        struct root_domain      *rd;
};

enum s_alloc {
        sa_rootdomain,
        sa_sd,
        sa_sd_storage,
        sa_none,
};

/*
 * Return the canonical balance CPU for this group, this is the first CPU
 * of this group that's also in the balance mask.
 *
 * The balance mask are all those CPUs that could actually end up at this
 * group. See build_balance_mask().
 *
 * Also see should_we_balance().
 */
int group_balance_cpu(struct sched_group *sg)
{
        return cpumask_first(group_balance_mask(sg));
}


/*
 * NUMA topology (first read the regular topology blurb below)
 *
 * Given a node-distance table, for example:
 *
 *   node   0   1   2   3
 *     0:  10  20  30  20
 *     1:  20  10  20  30
 *     2:  30  20  10  20
 *     3:  20  30  20  10
 *
 * which represents a 4 node ring topology like:
 *
 *   0 ----- 1
 *   |       |
 *   |       |
 *   |       |
 *   3 ----- 2
 *
 * We want to construct domains and groups to represent this. The way we go
 * about doing this is to build the domains on 'hops'. For each NUMA level we
 * construct the mask of all nodes reachable in @level hops.
 *
 * For the above NUMA topology that gives 3 levels:
 *
 * NUMA-2       0-3             0-3             0-3             0-3
 *  groups:     {0-1,3},{1-3}   {0-2},{0,2-3}   {1-3},{0-1,3}   {0,2-3},{0-2}
 *
 * NUMA-1       0-1,3           0-2             1-3             0,2-3
 *  groups:     {0},{1},{3}     {0},{1},{2}     {1},{2},{3}     {0},{2},{3}
 *
 * NUMA-0       0               1               2               3
 *
 *
 * As can be seen; things don't nicely line up as with the regular topology.
 * When we iterate a domain in child domain chunks some nodes can be
 * represented multiple times -- hence the "overlap" naming for this part of
 * the topology.
 *
 * In order to minimize this overlap, we only build enough groups to cover the
 * domain. For instance Node-0 NUMA-2 would only get groups: 0-1,3 and 1-3.
 *
 * Because:
 *
 *  - the first group of each domain is its child domain; this
 *    gets us the first 0-1,3
 *  - the only uncovered node is 2, who's child domain is 1-3.
 *
 * However, because of the overlap, computing a unique CPU for each group is
 * more complicated. Consider for instance the groups of NODE-1 NUMA-2, both
 * groups include the CPUs of Node-0, while those CPUs would not in fact ever
 * end up at those groups (they would end up in group: 0-1,3).
 *
 * To correct this we have to introduce the group balance mask. This mask
 * will contain those CPUs in the group that can reach this group given the
 * (child) domain tree.
 *
 * With this we can once again compute balance_cpu and sched_group_capacity
 * relations.
 *
 * XXX include words on how balance_cpu is unique and therefore can be
 * used for sched_group_capacity links.
 *
 *
 * Another 'interesting' topology is:
 *
 *   node   0   1   2   3
 *     0:  10  20  20  30
 *     1:  20  10  20  20
 *     2:  20  20  10  20
 *     3:  30  20  20  10
 *
 * Which looks a little like:
 *
 *   0 ----- 1
 *   |     / |
 *   |   /   |
 *   | /     |
 *   2 ----- 3
 *
 * This topology is asymmetric, nodes 1,2 are fully connected, but nodes 0,3
 * are not.
 *
 * This leads to a few particularly weird cases where the sched_domain's are
 * not of the same number for each cpu. Consider:
 *
 * NUMA-2       0-3                                             0-3
 *  groups:     {0-2},{1-3}                                     {1-3},{0-2}
 *
 * NUMA-1       0-2             0-3             0-3             1-3
 *
 * NUMA-0       0               1               2               3
 *
 */


/*
 * Build the balance mask; it contains only those CPUs that can arrive at this
 * group and should be considered to continue balancing.
 *
 * We do this during the group creation pass, therefore the group information
 * isn't complete yet, however since each group represents a (child) domain we
 * can fully construct this using the sched_domain bits (which are already
 * complete).
 */
static void
build_balance_mask(struct sched_domain *sd, struct sched_group *sg, struct cpumask *mask)
{
        const struct cpumask *sg_span = sched_group_span(sg);
        struct sd_data *sdd = sd->private;
        struct sched_domain *sibling;
        int i;

        cpumask_clear(mask);

        for_each_cpu(i, sg_span) {
                sibling = *per_cpu_ptr(sdd->sd, i);

                /*
                 * Can happen in the asymmetric case, where these siblings are
                 * unused. The mask will not be empty because those CPUs that
                 * do have the top domain _should_ span the domain.
                 */
                if (!sibling->child)
                        continue;

                /* If we would not end up here, we can't continue from here */
                if (!cpumask_equal(sg_span, sched_domain_span(sibling->child)))
                        continue;

                cpumask_set_cpu(i, mask);
        }

        /* We must not have empty masks here */
        WARN_ON_ONCE(cpumask_empty(mask));
}

/*
 * XXX: This creates per-node group entries; since the load-balancer will
 * immediately access remote memory to construct this group's load-balance
 * statistics having the groups node local is of dubious benefit.
 */
static struct sched_group *
build_group_from_child_sched_domain(struct sched_domain *sd, int cpu)
{
        struct sched_group *sg;
        struct cpumask *sg_span;

        sg = kzalloc_node(sizeof(struct sched_group) + cpumask_size(),
                        GFP_KERNEL, cpu_to_node(cpu));

        if (!sg)
                return NULL;

        sg_span = sched_group_span(sg);
        if (sd->child)
                cpumask_copy(sg_span, sched_domain_span(sd->child));
        else
                cpumask_copy(sg_span, sched_domain_span(sd));

        atomic_inc(&sg->ref);
        return sg;
}

static void init_overlap_sched_group(struct sched_domain *sd,
                                     struct sched_group *sg)
{
        struct cpumask *mask = sched_domains_tmpmask2;
        struct sd_data *sdd = sd->private;
        struct cpumask *sg_span;
        int cpu;

        build_balance_mask(sd, sg, mask);
        cpu = cpumask_first_and(sched_group_span(sg), mask);

        sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);
        if (atomic_inc_return(&sg->sgc->ref) == 1)
                cpumask_copy(group_balance_mask(sg), mask);
        else
                WARN_ON_ONCE(!cpumask_equal(group_balance_mask(sg), mask));

        /*
         * Initialize sgc->capacity such that even if we mess up the
         * domains and no possible iteration will get us here, we won't
         * die on a /0 trap.
         */
        sg_span = sched_group_span(sg);
        sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sg_span);
        sg->sgc->min_capacity = SCHED_CAPACITY_SCALE;
}

static int
build_overlap_sched_groups(struct sched_domain *sd, int cpu)
{
        struct sched_group *first = NULL, *last = NULL, *sg;
        const struct cpumask *span = sched_domain_span(sd);
        struct cpumask *covered = sched_domains_tmpmask;
        struct sd_data *sdd = sd->private;
        struct sched_domain *sibling;
        int i;

        cpumask_clear(covered);

        for_each_cpu_wrap(i, span, cpu) {
                struct cpumask *sg_span;

                if (cpumask_test_cpu(i, covered))
                        continue;

                sibling = *per_cpu_ptr(sdd->sd, i);

                /*
                 * Asymmetric node setups can result in situations where the
                 * domain tree is of unequal depth, make sure to skip domains
                 * that already cover the entire range.
                 *
                 * In that case build_sched_domains() will have terminated the
                 * iteration early and our sibling sd spans will be empty.
                 * Domains should always include the CPU they're built on, so
                 * check that.
                 */
                if (!cpumask_test_cpu(i, sched_domain_span(sibling)))
                        continue;

                sg = build_group_from_child_sched_domain(sibling, cpu);
                if (!sg)
                        goto fail;

                sg_span = sched_group_span(sg);
                cpumask_or(covered, covered, sg_span);

                init_overlap_sched_group(sd, sg);

                if (!first)
                        first = sg;
                if (last)
                        last->next = sg;
                last = sg;
                last->next = first;
        }
        sd->groups = first;

        return 0;

fail:
        free_sched_groups(first, 0);

        return -ENOMEM;
}


/*
 * Package topology (also see the load-balance blurb in fair.c)
 *
 * The scheduler builds a tree structure to represent a number of important
 * topology features. By default (default_topology[]) these include:
 *
 *  - Simultaneous multithreading (SMT)
 *  - Multi-Core Cache (MC)
 *  - Package (DIE)
 *
 * Where the last one more or less denotes everything up to a NUMA node.
 *
 * The tree consists of 3 primary data structures:
 *
 *      sched_domain -> sched_group -> sched_group_capacity
 *          ^ ^             ^ ^
 *          `-'             `-'
 *
 * The sched_domains are per-cpu and have a two way link (parent & child) and
 * denote the ever growing mask of CPUs belonging to that level of topology.
 *
 * Each sched_domain has a circular (double) linked list of sched_group's, each
 * denoting the domains of the level below (or individual CPUs in case of the
 * first domain level). The sched_group linked by a sched_domain includes the
 * CPU of that sched_domain [*].
 *
 * Take for instance a 2 threaded, 2 core, 2 cache cluster part:
 *
 * CPU   0   1   2   3   4   5   6   7
 *
 * DIE  [                             ]
 * MC   [             ] [             ]
 * SMT  [     ] [     ] [     ] [     ]
 *
 *  - or -
 *
 * DIE  0-7 0-7 0-7 0-7 0-7 0-7 0-7 0-7
 * MC   0-3 0-3 0-3 0-3 4-7 4-7 4-7 4-7
 * SMT  0-1 0-1 2-3 2-3 4-5 4-5 6-7 6-7
 *
 * CPU   0   1   2   3   4   5   6   7
 *
 * One way to think about it is: sched_domain moves you up and down among these
 * topology levels, while sched_group moves you sideways through it, at child
 * domain granularity.
 *
 * sched_group_capacity ensures each unique sched_group has shared storage.
 *
 * There are two related construction problems, both require a CPU that
 * uniquely identify each group (for a given domain):
 *
 *  - The first is the balance_cpu (see should_we_balance() and the
 *    load-balance blub in fair.c); for each group we only want 1 CPU to
 *    continue balancing at a higher domain.
 *
 *  - The second is the sched_group_capacity; we want all identical groups
 *    to share a single sched_group_capacity.
 *
 * Since these topologies are exclusive by construction. That is, its
 * impossible for an SMT thread to belong to multiple cores, and cores to
 * be part of multiple caches. There is a very clear and unique location
 * for each CPU in the hierarchy.
 *
 * Therefore computing a unique CPU for each group is trivial (the iteration
 * mask is redundant and set all 1s; all CPUs in a group will end up at _that_
 * group), we can simply pick the first CPU in each group.
 *
 *
 * [*] in other words, the first group of each domain is its child domain.
 */

static struct sched_group *get_group(int cpu, struct sd_data *sdd)
{
        struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
        struct sched_domain *child = sd->child;
        struct sched_group *sg;

        if (child)
                cpu = cpumask_first(sched_domain_span(child));

        sg = *per_cpu_ptr(sdd->sg, cpu);
        sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);

        /* For claim_allocations: */
        atomic_inc(&sg->ref);
        atomic_inc(&sg->sgc->ref);

        if (child) {
                cpumask_copy(sched_group_span(sg), sched_domain_span(child));
                cpumask_copy(group_balance_mask(sg), sched_group_span(sg));
        } else {
                cpumask_set_cpu(cpu, sched_group_span(sg));
                cpumask_set_cpu(cpu, group_balance_mask(sg));
        }

        sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sched_group_span(sg));
        sg->sgc->min_capacity = SCHED_CAPACITY_SCALE;

        return sg;
}

/*
 * build_sched_groups will build a circular linked list of the groups
 * covered by the given span, and will set each group's ->cpumask correctly,
 * and ->cpu_capacity to 0.
 *
 * Assumes the sched_domain tree is fully constructed
 */
static int
build_sched_groups(struct sched_domain *sd, int cpu)
{
        struct sched_group *first = NULL, *last = NULL;
        struct sd_data *sdd = sd->private;
        const struct cpumask *span = sched_domain_span(sd);
        struct cpumask *covered;
        int i;

        lockdep_assert_held(&sched_domains_mutex);
        covered = sched_domains_tmpmask;

        cpumask_clear(covered);

        for_each_cpu_wrap(i, span, cpu) {
                struct sched_group *sg;

                if (cpumask_test_cpu(i, covered))
                        continue;

                sg = get_group(i, sdd);

                cpumask_or(covered, covered, sched_group_span(sg));

                if (!first)
                        first = sg;
                if (last)
                        last->next = sg;
                last = sg;
        }
        last->next = first;
        sd->groups = first;

        return 0;
}

/*
 * Initialize sched groups cpu_capacity.
 *
 * cpu_capacity indicates the capacity of sched group, which is used while
 * distributing the load between different sched groups in a sched domain.
 * Typically cpu_capacity for all the groups in a sched domain will be same
 * unless there are asymmetries in the topology. If there are asymmetries,
 * group having more cpu_capacity will pickup more load compared to the
 * group having less cpu_capacity.
 */
static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
{
        struct sched_group *sg = sd->groups;

        WARN_ON(!sg);

        do {
                int cpu, max_cpu = -1;

                sg->group_weight = cpumask_weight(sched_group_span(sg));

                if (!(sd->flags & SD_ASYM_PACKING))
                        goto next;

                for_each_cpu(cpu, sched_group_span(sg)) {
                        if (max_cpu < 0)
                                max_cpu = cpu;
                        else if (sched_asym_prefer(cpu, max_cpu))
                                max_cpu = cpu;
                }
                sg->asym_prefer_cpu = max_cpu;

next:
                sg = sg->next;
        } while (sg != sd->groups);

        if (cpu != group_balance_cpu(sg))
                return;

        update_group_capacity(sd, cpu);
}

/*
 * Initializers for schedule domains
 * Non-inlined to reduce accumulated stack pressure in build_sched_domains()
 */

static int default_relax_domain_level = -1;
int sched_domain_level_max;

static int __init setup_relax_domain_level(char *str)
{
        if (kstrtoint(str, 0, &default_relax_domain_level))
                pr_warn("Unable to set relax_domain_level\n");

        return 1;
}
__setup("relax_domain_level=", setup_relax_domain_level);

static void set_domain_attribute(struct sched_domain *sd,
                                 struct sched_domain_attr *attr)
{
        int request;

        if (!attr || attr->relax_domain_level < 0) {
                if (default_relax_domain_level < 0)
                        return;
                else
                        request = default_relax_domain_level;
        } else
                request = attr->relax_domain_level;
        if (request < sd->level) {
                /* Turn off idle balance on this domain: */
                sd->flags &= ~(SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
        } else {
                /* Turn on idle balance on this domain: */
                sd->flags |= (SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
        }
}

static void __sdt_free(const struct cpumask *cpu_map);
static int __sdt_alloc(const struct cpumask *cpu_map);

static void __free_domain_allocs(struct s_data *d, enum s_alloc what,
                                 const struct cpumask *cpu_map)
{
        switch (what) {
        case sa_rootdomain:
                if (!atomic_read(&d->rd->refcount))
                        free_rootdomain(&d->rd->rcu);
                /* Fall through */
        case sa_sd:
                free_percpu(d->sd);
                /* Fall through */
        case sa_sd_storage:
                __sdt_free(cpu_map);
                /* Fall through */
        case sa_none:
                break;
        }
}

static enum s_alloc
__visit_domain_allocation_hell(struct s_data *d, const struct cpumask *cpu_map)
{
        memset(d, 0, sizeof(*d));

        if (__sdt_alloc(cpu_map))
                return sa_sd_storage;
        d->sd = alloc_percpu(struct sched_domain *);
        if (!d->sd)
                return sa_sd_storage;
        d->rd = alloc_rootdomain();
        if (!d->rd)
                return sa_sd;
        return sa_rootdomain;
}

/*
 * NULL the sd_data elements we've used to build the sched_domain and
 * sched_group structure so that the subsequent __free_domain_allocs()
 * will not free the data we're using.
 */
static void claim_allocations(int cpu, struct sched_domain *sd)
{
        struct sd_data *sdd = sd->private;

        WARN_ON_ONCE(*per_cpu_ptr(sdd->sd, cpu) != sd);
        *per_cpu_ptr(sdd->sd, cpu) = NULL;

        if (atomic_read(&(*per_cpu_ptr(sdd->sds, cpu))->ref))
                *per_cpu_ptr(sdd->sds, cpu) = NULL;

        if (atomic_read(&(*per_cpu_ptr(sdd->sg, cpu))->ref))
                *per_cpu_ptr(sdd->sg, cpu) = NULL;

        if (atomic_read(&(*per_cpu_ptr(sdd->sgc, cpu))->ref))
                *per_cpu_ptr(sdd->sgc, cpu) = NULL;
}

#ifdef CONFIG_NUMA
static int sched_domains_numa_levels;
enum numa_topology_type sched_numa_topology_type;
static int *sched_domains_numa_distance;
int sched_max_numa_distance;
static struct cpumask ***sched_domains_numa_masks;
static int sched_domains_curr_level;
#endif

/*
 * SD_flags allowed in topology descriptions.
 *
 * These flags are purely descriptive of the topology and do not prescribe
 * behaviour. Behaviour is artificial and mapped in the below sd_init()
 * function:
 *
 *   SD_SHARE_CPUCAPACITY   - describes SMT topologies
 *   SD_SHARE_PKG_RESOURCES - describes shared caches
 *   SD_NUMA                - describes NUMA topologies
 *   SD_SHARE_POWERDOMAIN   - describes shared power domain
 *   SD_ASYM_CPUCAPACITY    - describes mixed capacity topologies
 *
 * Odd one out, which beside describing the topology has a quirk also
 * prescribes the desired behaviour that goes along with it:
 *
 *   SD_ASYM_PACKING        - describes SMT quirks
 */
#define TOPOLOGY_SD_FLAGS               \
        (SD_SHARE_CPUCAPACITY |         \
         SD_SHARE_PKG_RESOURCES |       \
         SD_NUMA |                      \
         SD_ASYM_PACKING |              \
         SD_ASYM_CPUCAPACITY |          \
         SD_SHARE_POWERDOMAIN)

static struct sched_domain *
sd_init(struct sched_domain_topology_level *tl,
        const struct cpumask *cpu_map,
        struct sched_domain *child, int cpu)
{
        struct sd_data *sdd = &tl->data;
        struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
        int sd_id, sd_weight, sd_flags = 0;

#ifdef CONFIG_NUMA
        /*
         * Ugly hack to pass state to sd_numa_mask()...
         */
        sched_domains_curr_level = tl->numa_level;
#endif

        sd_weight = cpumask_weight(tl->mask(cpu));

        if (tl->sd_flags)
                sd_flags = (*tl->sd_flags)();
        if (WARN_ONCE(sd_flags & ~TOPOLOGY_SD_FLAGS,
                        "wrong sd_flags in topology description\n"))
                sd_flags &= ~TOPOLOGY_SD_FLAGS;

        *sd = (struct sched_domain){
                .min_interval           = sd_weight,
                .max_interval           = 2*sd_weight,
                .busy_factor            = 32,
                .imbalance_pct          = 125,

                .cache_nice_tries       = 0,
                .busy_idx               = 0,
                .idle_idx               = 0,
                .newidle_idx            = 0,
                .wake_idx               = 0,
                .forkexec_idx           = 0,

                .flags                  = 1*SD_LOAD_BALANCE
                                        | 1*SD_BALANCE_NEWIDLE
                                        | 1*SD_BALANCE_EXEC
                                        | 1*SD_BALANCE_FORK
                                        | 0*SD_BALANCE_WAKE
                                        | 1*SD_WAKE_AFFINE
                                        | 0*SD_SHARE_CPUCAPACITY
                                        | 0*SD_SHARE_PKG_RESOURCES
                                        | 0*SD_SERIALIZE
                                        | 0*SD_PREFER_SIBLING
                                        | 0*SD_NUMA
                                        | sd_flags
                                        ,

                .last_balance           = jiffies,
                .balance_interval       = sd_weight,
                .smt_gain               = 0,
                .max_newidle_lb_cost    = 0,
                .next_decay_max_lb_cost = jiffies,
                .child                  = child,
#ifdef CONFIG_SCHED_DEBUG
                .name                   = tl->name,
#endif
        };

        cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu));
        sd_id = cpumask_first(sched_domain_span(sd));

        /*
         * Convert topological properties into behaviour.
         */

        if (sd->flags & SD_ASYM_CPUCAPACITY) {
                struct sched_domain *t = sd;

                for_each_lower_domain(t)
                        t->flags |= SD_BALANCE_WAKE;
        }

        if (sd->flags & SD_SHARE_CPUCAPACITY) {
                sd->flags |= SD_PREFER_SIBLING;
                sd->imbalance_pct = 110;
                sd->smt_gain = 1178; /* ~15% */

        } else if (sd->flags & SD_SHARE_PKG_RESOURCES) {
                sd->imbalance_pct = 117;
                sd->cache_nice_tries = 1;
                sd->busy_idx = 2;

#ifdef CONFIG_NUMA
        } else if (sd->flags & SD_NUMA) {
                sd->cache_nice_tries = 2;
                sd->busy_idx = 3;
                sd->idle_idx = 2;

                sd->flags |= SD_SERIALIZE;
                if (sched_domains_numa_distance[tl->numa_level] > RECLAIM_DISTANCE) {
                        sd->flags &= ~(SD_BALANCE_EXEC |
                                       SD_BALANCE_FORK |
                                       SD_WAKE_AFFINE);
                }

#endif
        } else {
                sd->flags |= SD_PREFER_SIBLING;
                sd->cache_nice_tries = 1;
                sd->busy_idx = 2;
                sd->idle_idx = 1;
        }

        /*
         * For all levels sharing cache; connect a sched_domain_shared
         * instance.
         */
        if (sd->flags & SD_SHARE_PKG_RESOURCES) {
                sd->shared = *per_cpu_ptr(sdd->sds, sd_id);
                atomic_inc(&sd->shared->ref);
                atomic_set(&sd->shared->nr_busy_cpus, sd_weight);
        }

        sd->private = sdd;

        return sd;
}

/*
 * Topology list, bottom-up.
 */
static struct sched_domain_topology_level default_topology[] = {
#ifdef CONFIG_SCHED_SMT
        { cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
#endif
#ifdef CONFIG_SCHED_MC
        { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
#endif
        { cpu_cpu_mask, SD_INIT_NAME(DIE) },
        { NULL, },
};

static struct sched_domain_topology_level *sched_domain_topology =
        default_topology;

#define for_each_sd_topology(tl)                        \
        for (tl = sched_domain_topology; tl->mask; tl++)

void set_sched_topology(struct sched_domain_topology_level *tl)
{
        if (WARN_ON_ONCE(sched_smp_initialized))
                return;

        sched_domain_topology = tl;
}

#ifdef CONFIG_NUMA

static const struct cpumask *sd_numa_mask(int cpu)
{
        return sched_domains_numa_masks[sched_domains_curr_level][cpu_to_node(cpu)];
}

static void sched_numa_warn(const char *str)
{
        static int done = false;
        int i,j;

        if (done)
                return;

        done = true;

        printk(KERN_WARNING "ERROR: %s\n\n", str);

        for (i = 0; i < nr_node_ids; i++) {
                printk(KERN_WARNING "  ");
                for (j = 0; j < nr_node_ids; j++)
                        printk(KERN_CONT "%02d ", node_distance(i,j));
                printk(KERN_CONT "\n");
        }
        printk(KERN_WARNING "\n");
}

bool find_numa_distance(int distance)
{
        int i;

        if (distance == node_distance(0, 0))
                return true;

        for (i = 0; i < sched_domains_numa_levels; i++) {
                if (sched_domains_numa_distance[i] == distance)
                        return true;
        }

        return false;
}

/*
 * A system can have three types of NUMA topology:
 * NUMA_DIRECT: all nodes are directly connected, or not a NUMA system
 * NUMA_GLUELESS_MESH: some nodes reachable through intermediary nodes
 * NUMA_BACKPLANE: nodes can reach other nodes through a backplane
 *
 * The difference between a glueless mesh topology and a backplane
 * topology lies in whether communication between not directly
 * connected nodes goes through intermediary nodes (where programs
 * could run), or through backplane controllers. This affects
 * placement of programs.
 *
 * The type of topology can be discerned with the following tests:
 * - If the maximum distance between any nodes is 1 hop, the system
 *   is directly connected.
 * - If for two nodes A and B, located N > 1 hops away from each other,
 *   there is an intermediary node C, which is < N hops away from both
 *   nodes A and B, the system is a glueless mesh.
 */
static void init_numa_topology_type(void)
{
        int a, b, c, n;

        n = sched_max_numa_distance;

        if (sched_domains_numa_levels <= 1) {
                sched_numa_topology_type = NUMA_DIRECT;
                return;
        }

        for_each_online_node(a) {
                for_each_online_node(b) {
                        /* Find two nodes furthest removed from each other. */
                        if (node_distance(a, b) < n)
                                continue;

                        /* Is there an intermediary node between a and b? */
                        for_each_online_node(c) {
                                if (node_distance(a, c) < n &&
                                    node_distance(b, c) < n) {
                                        sched_numa_topology_type =
                                                        NUMA_GLUELESS_MESH;
                                        return;
                                }
                        }

                        sched_numa_topology_type = NUMA_BACKPLANE;
                        return;
                }
        }
}

void sched_init_numa(void)
{
        int next_distance, curr_distance = node_distance(0, 0);
        struct sched_domain_topology_level *tl;
        int level = 0;
        int i, j, k;

        sched_domains_numa_distance = kzalloc(sizeof(int) * nr_node_ids, GFP_KERNEL);
        if (!sched_domains_numa_distance)
                return;

        /*
         * O(nr_nodes^2) deduplicating selection sort -- in order to find the
         * unique distances in the node_distance() table.
         *
         * Assumes node_distance(0,j) includes all distances in
         * node_distance(i,j) in order to avoid cubic time.
         */
        next_distance = curr_distance;
        for (i = 0; i < nr_node_ids; i++) {
                for (j = 0; j < nr_node_ids; j++) {
                        for (k = 0; k < nr_node_ids; k++) {
                                int distance = node_distance(i, k);

                                if (distance > curr_distance &&
                                    (distance < next_distance ||
                                     next_distance == curr_distance))
                                        next_distance = distance;

                                /*
                                 * While not a strong assumption it would be nice to know
                                 * about cases where if node A is connected to B, B is not
                                 * equally connected to A.
                                 */
                                if (sched_debug() && node_distance(k, i) != distance)
                                        sched_numa_warn("Node-distance not symmetric");

                                if (sched_debug() && i && !find_numa_distance(distance))
                                        sched_numa_warn("Node-0 not representative");
                        }
                        if (next_distance != curr_distance) {
                                sched_domains_numa_distance[level++] = next_distance;
                                sched_domains_numa_levels = level;
                                curr_distance = next_distance;
                        } else break;
                }

                /*
                 * In case of sched_debug() we verify the above assumption.
                 */
                if (!sched_debug())
                        break;
        }

        if (!level)
                return;

        /*
         * 'level' contains the number of unique distances, excluding the
         * identity distance node_distance(i,i).
         *
         * The sched_domains_numa_distance[] array includes the actual distance
         * numbers.
         */

        /*
         * Here, we should temporarily reset sched_domains_numa_levels to 0.
         * If it fails to allocate memory for array sched_domains_numa_masks[][],
         * the array will contain less then 'level' members. This could be
         * dangerous when we use it to iterate array sched_domains_numa_masks[][]
         * in other functions.
         *
         * We reset it to 'level' at the end of this function.
         */
        sched_domains_numa_levels = 0;

        sched_domains_numa_masks = kzalloc(sizeof(void *) * level, GFP_KERNEL);
        if (!sched_domains_numa_masks)
                return;

        /*
         * Now for each level, construct a mask per node which contains all
         * CPUs of nodes that are that many hops away from us.
         */
        for (i = 0; i < level; i++) {
                sched_domains_numa_masks[i] =
                        kzalloc(nr_node_ids * sizeof(void *), GFP_KERNEL);
                if (!sched_domains_numa_masks[i])
                        return;

                for (j = 0; j < nr_node_ids; j++) {
                        struct cpumask *mask = kzalloc(cpumask_size(), GFP_KERNEL);
                        if (!mask)
                                return;

                        sched_domains_numa_masks[i][j] = mask;

                        for_each_node(k) {
                                if (node_distance(j, k) > sched_domains_numa_distance[i])
                                        continue;

                                cpumask_or(mask, mask, cpumask_of_node(k));
                        }
                }
        }

        /* Compute default topology size */
        for (i = 0; sched_domain_topology[i].mask; i++);

        tl = kzalloc((i + level + 1) *
                        sizeof(struct sched_domain_topology_level), GFP_KERNEL);
        if (!tl)
                return;

        /*
         * Copy the default topology bits..
         */
        for (i = 0; sched_domain_topology[i].mask; i++)
                tl[i] = sched_domain_topology[i];

        /*
         * .. and append 'j' levels of NUMA goodness.
         */
        for (j = 0; j < level; i++, j++) {
                tl[i] = (struct sched_domain_topology_level){
                        .mask = sd_numa_mask,
                        .sd_flags = cpu_numa_flags,
                        .flags = SDTL_OVERLAP,
                        .numa_level = j,
                        SD_INIT_NAME(NUMA)
                };
        }

        sched_domain_topology = tl;

        sched_domains_numa_levels = level;
        sched_max_numa_distance = sched_domains_numa_distance[level - 1];

        init_numa_topology_type();
}

void sched_domains_numa_masks_set(unsigned int cpu)
{
        int node = cpu_to_node(cpu);
        int i, j;

        for (i = 0; i < sched_domains_numa_levels; i++) {
                for (j = 0; j < nr_node_ids; j++) {
                        if (node_distance(j, node) <= sched_domains_numa_distance[i])
                                cpumask_set_cpu(cpu, sched_domains_numa_masks[i][j]);
                }
        }
}

void sched_domains_numa_masks_clear(unsigned int cpu)
{
        int i, j;

        for (i = 0; i < sched_domains_numa_levels; i++) {
                for (j = 0; j < nr_node_ids; j++)
                        cpumask_clear_cpu(cpu, sched_domains_numa_masks[i][j]);
        }
}

#endif /* CONFIG_NUMA */

static int __sdt_alloc(const struct cpumask *cpu_map)
{
        struct sched_domain_topology_level *tl;
        int j;

        for_each_sd_topology(tl) {
                struct sd_data *sdd = &tl->data;

                sdd->sd = alloc_percpu(struct sched_domain *);
                if (!sdd->sd)
                        return -ENOMEM;

                sdd->sds = alloc_percpu(struct sched_domain_shared *);
                if (!sdd->sds)
                        return -ENOMEM;

                sdd->sg = alloc_percpu(struct sched_group *);
                if (!sdd->sg)
                        return -ENOMEM;

                sdd->sgc = alloc_percpu(struct sched_group_capacity *);
                if (!sdd->sgc)
                        return -ENOMEM;

                for_each_cpu(j, cpu_map) {
                        struct sched_domain *sd;
                        struct sched_domain_shared *sds;
                        struct sched_group *sg;
                        struct sched_group_capacity *sgc;

                        sd = kzalloc_node(sizeof(struct sched_domain) + cpumask_size(),
                                        GFP_KERNEL, cpu_to_node(j));
                        if (!sd)
                                return -ENOMEM;

                        *per_cpu_ptr(sdd->sd, j) = sd;

                        sds = kzalloc_node(sizeof(struct sched_domain_shared),
                                        GFP_KERNEL, cpu_to_node(j));
                        if (!sds)
                                return -ENOMEM;

                        *per_cpu_ptr(sdd->sds, j) = sds;

                        sg = kzalloc_node(sizeof(struct sched_group) + cpumask_size(),
                                        GFP_KERNEL, cpu_to_node(j));
                        if (!sg)
                                return -ENOMEM;

                        sg->next = sg;

                        *per_cpu_ptr(sdd->sg, j) = sg;

                        sgc = kzalloc_node(sizeof(struct sched_group_capacity) + cpumask_size(),
                                        GFP_KERNEL, cpu_to_node(j));
                        if (!sgc)
                                return -ENOMEM;

#ifdef CONFIG_SCHED_DEBUG
                        sgc->id = j;
#endif

                        *per_cpu_ptr(sdd->sgc, j) = sgc;
                }
        }

        return 0;
}

static void __sdt_free(const struct cpumask *cpu_map)
{
        struct sched_domain_topology_level *tl;
        int j;

        for_each_sd_topology(tl) {
                struct sd_data *sdd = &tl->data;

                for_each_cpu(j, cpu_map) {
                        struct sched_domain *sd;

                        if (sdd->sd) {
                                sd = *per_cpu_ptr(sdd->sd, j);
                                if (sd && (sd->flags & SD_OVERLAP))
                                        free_sched_groups(sd->groups, 0);
                                kfree(*per_cpu_ptr(sdd->sd, j));
                        }

                        if (sdd->sds)
                                kfree(*per_cpu_ptr(sdd->sds, j));
                        if (sdd->sg)
                                kfree(*per_cpu_ptr(sdd->sg, j));
                        if (sdd->sgc)
                                kfree(*per_cpu_ptr(sdd->sgc, j));
                }
                free_percpu(sdd->sd);
                sdd->sd = NULL;
                free_percpu(sdd->sds);
                sdd->sds = NULL;
                free_percpu(sdd->sg);
                sdd->sg = NULL;
                free_percpu(sdd->sgc);
                sdd->sgc = NULL;
        }
}

static struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl,
                const struct cpumask *cpu_map, struct sched_domain_attr *attr,
                struct sched_domain *child, int cpu)
{
        struct sched_domain *sd = sd_init(tl, cpu_map, child, cpu);

        if (child) {
                sd->level = child->level + 1;
                sched_domain_level_max = max(sched_domain_level_max, sd->level);
                child->parent = sd;

                if (!cpumask_subset(sched_domain_span(child),
                                    sched_domain_span(sd))) {
                        pr_err("BUG: arch topology borken\n");
#ifdef CONFIG_SCHED_DEBUG
                        pr_err("     the %s domain not a subset of the %s domain\n",
                                        child->name, sd->name);
#endif
                        /* Fixup, ensure @sd has at least @child cpus. */
                        cpumask_or(sched_domain_span(sd),
                                   sched_domain_span(sd),
                                   sched_domain_span(child));
                }

        }
        set_domain_attribute(sd, attr);

        return sd;
}

/*
 * Build sched domains for a given set of CPUs and attach the sched domains
 * to the individual CPUs
 */
static int
build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *attr)
{
        enum s_alloc alloc_state;
        struct sched_domain *sd;
        struct s_data d;
        struct rq *rq = NULL;
        int i, ret = -ENOMEM;

        alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
        if (alloc_state != sa_rootdomain)
                goto error;

        /* Set up domains for CPUs specified by the cpu_map: */
        for_each_cpu(i, cpu_map) {
                struct sched_domain_topology_level *tl;

                sd = NULL;
                for_each_sd_topology(tl) {
                        sd = build_sched_domain(tl, cpu_map, attr, sd, i);
                        if (tl == sched_domain_topology)
                                *per_cpu_ptr(d.sd, i) = sd;
                        if (tl->flags & SDTL_OVERLAP)
                                sd->flags |= SD_OVERLAP;
                        if (cpumask_equal(cpu_map, sched_domain_span(sd)))
                                break;
                }
        }

        /* Build the groups for the domains */
        for_each_cpu(i, cpu_map) {
                for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
                        sd->span_weight = cpumask_weight(sched_domain_span(sd));
                        if (sd->flags & SD_OVERLAP) {
                                if (build_overlap_sched_groups(sd, i))
                                        goto error;
                        } else {
                                if (build_sched_groups(sd, i))
                                        goto error;
                        }
                }
        }

        /* Calculate CPU capacity for physical packages and nodes */
        for (i = nr_cpumask_bits-1; i >= 0; i--) {
                if (!cpumask_test_cpu(i, cpu_map))
                        continue;

                for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
                        claim_allocations(i, sd);
                        init_sched_groups_capacity(i, sd);
                }
        }

        /* Attach the domains */
        rcu_read_lock();
        for_each_cpu(i, cpu_map) {
                rq = cpu_rq(i);
                sd = *per_cpu_ptr(d.sd, i);

                /* Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing: */
                if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))
                        WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);

                cpu_attach_domain(sd, d.rd, i);
        }
        rcu_read_unlock();

        if (rq && sched_debug_enabled) {
                pr_info("span: %*pbl (max cpu_capacity = %lu)\n",
                        cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
        }

        ret = 0;
error:
        __free_domain_allocs(&d, alloc_state, cpu_map);
        return ret;
}

/* Current sched domains: */
static cpumask_var_t                    *doms_cur;

/* Number of sched domains in 'doms_cur': */
static int                              ndoms_cur;

/* Attribues of custom domains in 'doms_cur' */
static struct sched_domain_attr         *dattr_cur;

/*
 * Special case: If a kmalloc() of a doms_cur partition (array of
 * cpumask) fails, then fallback to a single sched domain,
 * as determined by the single cpumask fallback_doms.
 */
static cpumask_var_t                    fallback_doms;

/*
 * arch_update_cpu_topology lets virtualized architectures update the
 * CPU core maps. It is supposed to return 1 if the topology changed
 * or 0 if it stayed the same.
 */
int __weak arch_update_cpu_topology(void)
{
        return 0;
}

cpumask_var_t *alloc_sched_domains(unsigned int ndoms)
{
        int i;
        cpumask_var_t *doms;

        doms = kmalloc(sizeof(*doms) * ndoms, GFP_KERNEL);
        if (!doms)
                return NULL;
        for (i = 0; i < ndoms; i++) {
                if (!alloc_cpumask_var(&doms[i], GFP_KERNEL)) {
                        free_sched_domains(doms, i);
                        return NULL;
                }
        }
        return doms;
}

void free_sched_domains(cpumask_var_t doms[], unsigned int ndoms)
{
        unsigned int i;
        for (i = 0; i < ndoms; i++)
                free_cpumask_var(doms[i]);
        kfree(doms);
}

/*
 * Set up scheduler domains and groups. Callers must hold the hotplug lock.
 * For now this just excludes isolated CPUs, but could be used to
 * exclude other special cases in the future.
 */
int sched_init_domains(const struct cpumask *cpu_map)
{
        int err;

        zalloc_cpumask_var(&sched_domains_tmpmask, GFP_KERNEL);
        zalloc_cpumask_var(&sched_domains_tmpmask2, GFP_KERNEL);
        zalloc_cpumask_var(&fallback_doms, GFP_KERNEL);

        arch_update_cpu_topology();
        ndoms_cur = 1;
        doms_cur = alloc_sched_domains(ndoms_cur);
        if (!doms_cur)
                doms_cur = &fallback_doms;
        cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map);
        err = build_sched_domains(doms_cur[0], NULL);
        register_sched_domain_sysctl();

        return err;
}

/*
 * Detach sched domains from a group of CPUs specified in cpu_map
 * These CPUs will now be attached to the NULL domain
 */
static void detach_destroy_domains(const struct cpumask *cpu_map)
{
        int i;

        rcu_read_lock();
        for_each_cpu(i, cpu_map)
                cpu_attach_domain(NULL, &def_root_domain, i);
        rcu_read_unlock();
}

/* handle null as "default" */
static int dattrs_equal(struct sched_domain_attr *cur, int idx_cur,
                        struct sched_domain_attr *new, int idx_new)
{
        struct sched_domain_attr tmp;

        /* Fast path: */
        if (!new && !cur)
                return 1;

        tmp = SD_ATTR_INIT;
        return !memcmp(cur ? (cur + idx_cur) : &tmp,
                        new ? (new + idx_new) : &tmp,
                        sizeof(struct sched_domain_attr));
}

/*
 * Partition sched domains as specified by the 'ndoms_new'
 * cpumasks in the array doms_new[] of cpumasks. This compares
 * doms_new[] to the current sched domain partitioning, doms_cur[].
 * It destroys each deleted domain and builds each new domain.
 *
 * 'doms_new' is an array of cpumask_var_t's of length 'ndoms_new'.
 * The masks don't intersect (don't overlap.) We should setup one
 * sched domain for each mask. CPUs not in any of the cpumasks will
 * not be load balanced. If the same cpumask appears both in the
 * current 'doms_cur' domains and in the new 'doms_new', we can leave
 * it as it is.
 *
 * The passed in 'doms_new' should be allocated using
 * alloc_sched_domains.  This routine takes ownership of it and will
 * free_sched_domains it when done with it. If the caller failed the
 * alloc call, then it can pass in doms_new == NULL && ndoms_new == 1,
 * and partition_sched_domains() will fallback to the single partition
 * 'fallback_doms', it also forces the domains to be rebuilt.
 *
 * If doms_new == NULL it will be replaced with cpu_online_mask.
 * ndoms_new == 0 is a special case for destroying existing domains,
 * and it will not create the default domain.
 *
 * Call with hotplug lock held
 */
void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
                             struct sched_domain_attr *dattr_new)
{
        int i, j, n;
        int new_topology;

        mutex_lock(&sched_domains_mutex);

        /* Always unregister in case we don't destroy any domains: */
        unregister_sched_domain_sysctl();

        /* Let the architecture update CPU core mappings: */
        new_topology = arch_update_cpu_topology();

        if (!doms_new) {
                WARN_ON_ONCE(dattr_new);
                n = 0;
                doms_new = alloc_sched_domains(1);
                if (doms_new) {
                        n = 1;
                        cpumask_andnot(doms_new[0], cpu_active_mask, cpu_isolated_map);
                }
        } else {
                n = ndoms_new;
        }

        /* Destroy deleted domains: */
        for (i = 0; i < ndoms_cur; i++) {
                for (j = 0; j < n && !new_topology; j++) {
                        if (cpumask_equal(doms_cur[i], doms_new[j])
                            && dattrs_equal(dattr_cur, i, dattr_new, j))
                                goto match1;
                }
                /* No match - a current sched domain not in new doms_new[] */
                detach_destroy_domains(doms_cur[i]);
match1:
                ;
        }

        n = ndoms_cur;
        if (!doms_new) {
                n = 0;
                doms_new = &fallback_doms;
                cpumask_andnot(doms_new[0], cpu_active_mask, cpu_isolated_map);
        }

        /* Build new domains: */
        for (i = 0; i < ndoms_new; i++) {
                for (j = 0; j < n && !new_topology; j++) {
                        if (cpumask_equal(doms_new[i], doms_cur[j])
                            && dattrs_equal(dattr_new, i, dattr_cur, j))
                                goto match2;
                }
                /* No match - add a new doms_new */
                build_sched_domains(doms_new[i], dattr_new ? dattr_new + i : NULL);
match2:
                ;
        }

        /* Remember the new sched domains: */
        if (doms_cur != &fallback_doms)
                free_sched_domains(doms_cur, ndoms_cur);

        kfree(dattr_cur);
        doms_cur = doms_new;
        dattr_cur = dattr_new;
        ndoms_cur = ndoms_new;

        register_sched_domain_sysctl();

        mutex_unlock(&sched_domains_mutex);
}