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/****************************************************************************
 * (C) 2005-2006 - Emmanuel Ackaouy - XenSource Inc.
 ****************************************************************************
 *
 *        File: common/csched_credit.c
 *      Author: Emmanuel Ackaouy
 *
 * Description: Credit-based SMP CPU scheduler
 */

#include <xen/config.h>
#include <xen/init.h>
#include <xen/lib.h>
#include <xen/sched.h>
#include <xen/domain.h>
#include <xen/delay.h>
#include <xen/event.h>
#include <xen/time.h>
#include <xen/sched-if.h>
#include <xen/softirq.h>
#include <asm/atomic.h>
#include <asm/div64.h>
#include <xen/errno.h>
#include <xen/keyhandler.h>
#include <xen/trace.h>


/*
 * Basic constants
 */
#define CSCHED_DEFAULT_WEIGHT       256
#define CSCHED_TICKS_PER_TSLICE     3
/* Default timeslice: 30ms */
#define CSCHED_DEFAULT_TSLICE_MS    30
#define CSCHED_CREDITS_PER_MSEC     10


/*
 * Priorities
 */
#define CSCHED_PRI_TS_BOOST      0      /* time-share waking up */
#define CSCHED_PRI_TS_UNDER     -1      /* time-share w/ credits */
#define CSCHED_PRI_TS_OVER      -2      /* time-share w/o credits */
#define CSCHED_PRI_IDLE         -64     /* idle */


/*
 * Flags
 */
#define CSCHED_FLAG_VCPU_PARKED    0x0  /* VCPU over capped credits */
#define CSCHED_FLAG_VCPU_YIELD     0x1  /* VCPU yielding */


/*
 * Useful macros
 */
#define CSCHED_PRIV(_ops)   \
    ((struct csched_private *)((_ops)->sched_data))
#define CSCHED_PCPU(_c)     \
    ((struct csched_pcpu *)per_cpu(schedule_data, _c).sched_priv)
#define CSCHED_VCPU(_vcpu)  ((struct csched_vcpu *) (_vcpu)->sched_priv)
#define CSCHED_DOM(_dom)    ((struct csched_dom *) (_dom)->sched_priv)
#define RUNQ(_cpu)          (&(CSCHED_PCPU(_cpu)->runq))
/* Is the first element of _cpu's runq its idle vcpu? */
#define IS_RUNQ_IDLE(_cpu)  (list_empty(RUNQ(_cpu)) || \
                             is_idle_vcpu(__runq_elem(RUNQ(_cpu)->next)->vcpu))


/*
 * CSCHED_STATS
 *
 * Manage very basic per-vCPU counters and stats.
 *
 * Useful for debugging live systems. The stats are displayed
 * with runq dumps ('r' on the Xen console).
 */
#ifdef SCHED_STATS

#define CSCHED_STATS

#define SCHED_VCPU_STATS_RESET(_V)                      \
    do                                                  \
    {                                                   \
        memset(&(_V)->stats, 0, sizeof((_V)->stats));   \
    } while ( 0 )

#define SCHED_VCPU_STAT_CRANK(_V, _X)       (((_V)->stats._X)++)

#define SCHED_VCPU_STAT_SET(_V, _X, _Y)     (((_V)->stats._X) = (_Y))

#else /* !SCHED_STATS */

#undef CSCHED_STATS

#define SCHED_VCPU_STATS_RESET(_V)         do {} while ( 0 )
#define SCHED_VCPU_STAT_CRANK(_V, _X)      do {} while ( 0 )
#define SCHED_VCPU_STAT_SET(_V, _X, _Y)    do {} while ( 0 )

#endif /* SCHED_STATS */


/*
 * Credit tracing events ("only" 512 available!). Check
 * include/public/trace.h for more details.
 */
#define TRC_CSCHED_SCHED_TASKLET TRC_SCHED_CLASS_EVT(CSCHED, 1)
#define TRC_CSCHED_ACCOUNT_START TRC_SCHED_CLASS_EVT(CSCHED, 2)
#define TRC_CSCHED_ACCOUNT_STOP  TRC_SCHED_CLASS_EVT(CSCHED, 3)
#define TRC_CSCHED_STOLEN_VCPU   TRC_SCHED_CLASS_EVT(CSCHED, 4)
#define TRC_CSCHED_PICKED_CPU    TRC_SCHED_CLASS_EVT(CSCHED, 5)
#define TRC_CSCHED_TICKLE        TRC_SCHED_CLASS_EVT(CSCHED, 6)


/*
 * Node Balancing
 */
#define CSCHED_BALANCE_NODE_AFFINITY    0
#define CSCHED_BALANCE_CPU_AFFINITY     1

/*
 * Boot parameters
 */
static int __read_mostly sched_credit_tslice_ms = CSCHED_DEFAULT_TSLICE_MS;
integer_param("sched_credit_tslice_ms", sched_credit_tslice_ms);

/*
 * Physical CPU
 */
struct csched_pcpu {
    struct list_head runq;
    uint32_t runq_sort_last;
    struct timer ticker;
    unsigned int tick;
    unsigned int idle_bias;
    /* Store this here to avoid having too many cpumask_var_t-s on stack */
    cpumask_var_t balance_mask;
};

/*
 * Convenience macro for accessing the per-PCPU cpumask we need for
 * implementing the two steps (vcpu and node affinity) balancing logic.
 * It is stored in csched_pcpu so that serialization is not an issue,
 * as there is a csched_pcpu for each PCPU and we always hold the
 * runqueue spin-lock when using this.
 */
#define csched_balance_mask (CSCHED_PCPU(smp_processor_id())->balance_mask)

/*
 * Virtual CPU
 */
struct csched_vcpu {
    struct list_head runq_elem;
    struct list_head active_vcpu_elem;
    struct csched_dom *sdom;
    struct vcpu *vcpu;
    atomic_t credit;
    unsigned int residual;
    s_time_t start_time;   /* When we were scheduled (used for credit) */
    unsigned flags;
    int16_t pri;
#ifdef CSCHED_STATS
    struct {
        int credit_last;
        uint32_t credit_incr;
        uint32_t state_active;
        uint32_t state_idle;
        uint32_t migrate_q;
        uint32_t migrate_r;
        uint32_t kicked_away;
    } stats;
#endif
};

/*
 * Domain
 */
struct csched_dom {
    struct list_head active_vcpu;
    struct list_head active_sdom_elem;
    struct domain *dom;
    /* cpumask translated from the domain's node-affinity.
     * Basically, the CPUs we prefer to be scheduled on. */
    cpumask_var_t node_affinity_cpumask;
    uint16_t active_vcpu_count;
    uint16_t weight;
    uint16_t cap;
};

/*
 * System-wide private data
 */
struct csched_private {
    /* lock for the whole pluggable scheduler, nests inside cpupool_lock */
    spinlock_t lock;
    struct list_head active_sdom;
    uint32_t ncpus;
    struct timer  master_ticker;
    unsigned int master;
    cpumask_var_t idlers;
    cpumask_var_t cpus;
    uint32_t weight;
    uint32_t credit;
    int credit_balance;
    uint32_t runq_sort;
    unsigned ratelimit_us;
    /* Period of master and tick in milliseconds */
    unsigned tslice_ms, tick_period_us, ticks_per_tslice;
    unsigned credits_per_tslice;
};

static void csched_tick(void *_cpu);
static void csched_acct(void *dummy);

static inline int
__vcpu_on_runq(struct csched_vcpu *svc)
{
    return !list_empty(&svc->runq_elem);
}

static inline struct csched_vcpu *
__runq_elem(struct list_head *elem)
{
    return list_entry(elem, struct csched_vcpu, runq_elem);
}

static inline void
__runq_insert(unsigned int cpu, struct csched_vcpu *svc)
{
    const struct list_head * const runq = RUNQ(cpu);
    struct list_head *iter;

    BUG_ON( __vcpu_on_runq(svc) );
    BUG_ON( cpu != svc->vcpu->processor );

    list_for_each( iter, runq )
    {
        const struct csched_vcpu * const iter_svc = __runq_elem(iter);
        if ( svc->pri > iter_svc->pri )
            break;
    }

    /* If the vcpu yielded, try to put it behind one lower-priority
     * runnable vcpu if we can.  The next runq_sort will bring it forward
     * within 30ms if the queue too long. */
    if ( test_bit(CSCHED_FLAG_VCPU_YIELD, &svc->flags)
         && __runq_elem(iter)->pri > CSCHED_PRI_IDLE )
    {
        iter=iter->next;

        /* Some sanity checks */
        BUG_ON(iter == runq);
    }

    list_add_tail(&svc->runq_elem, iter);
}

static inline void
__runq_remove(struct csched_vcpu *svc)
{
    BUG_ON( !__vcpu_on_runq(svc) );
    list_del_init(&svc->runq_elem);
}

/*
 * Translates node-affinity mask into a cpumask, so that we can use it during
 * actual scheduling. That of course will contain all the cpus from all the
 * set nodes in the original node-affinity mask.
 *
 * Note that any serialization needed to access mask safely is complete
 * responsibility of the caller of this function/hook.
 */
static void csched_set_node_affinity(
    const struct scheduler *ops,
    struct domain *d,
    nodemask_t *mask)
{
    struct csched_dom *sdom;
    int node;

    /* Skip idle domain since it doesn't even have a node_affinity_cpumask */
    if ( unlikely(is_idle_domain(d)) )
        return;

    sdom = CSCHED_DOM(d);
    cpumask_clear(sdom->node_affinity_cpumask);
    for_each_node_mask( node, *mask )
        cpumask_or(sdom->node_affinity_cpumask, sdom->node_affinity_cpumask,
                   &node_to_cpumask(node));
}

#define for_each_csched_balance_step(step) \
    for ( (step) = 0; (step) <= CSCHED_BALANCE_CPU_AFFINITY; (step)++ )


/*
 * vcpu-affinity balancing is always necessary and must never be skipped.
 * OTOH, if a domain's node-affinity is said to be automatically computed
 * (or if it just spans all the nodes), we can safely avoid dealing with
 * node-affinity entirely. Ah, node-affinity is also deemed meaningless
 * in case it has empty intersection with the vcpu's vcpu-affinity, as it
 * would mean trying to schedule it on _no_ pcpu!
 */
#define __vcpu_has_node_affinity(vc)                                          \
    ( !(cpumask_full(CSCHED_DOM(vc->domain)->node_affinity_cpumask)           \
        || !cpumask_intersects(vc->cpu_affinity,                              \
                               CSCHED_DOM(vc->domain)->node_affinity_cpumask) \
        || vc->domain->auto_node_affinity == 1) )

/*
 * Each csched-balance step uses its own cpumask. This function determines
 * which one (given the step) and copies it in mask. For the node-affinity
 * balancing step, the pcpus that are not part of vc's vcpu-affinity are
 * filtered out from the result, to avoid running a vcpu where it would
 * like, but is not allowed to!
 */
static void
csched_balance_cpumask(const struct vcpu *vc, int step, cpumask_t *mask)
{
    if ( step == CSCHED_BALANCE_NODE_AFFINITY )
    {
        cpumask_and(mask, CSCHED_DOM(vc->domain)->node_affinity_cpumask,
                    vc->cpu_affinity);

        if ( unlikely(cpumask_empty(mask)) )
            cpumask_copy(mask, vc->cpu_affinity);
    }
    else /* step == CSCHED_BALANCE_CPU_AFFINITY */
        cpumask_copy(mask, vc->cpu_affinity);
}

static void burn_credits(struct csched_vcpu *svc, s_time_t now)
{
    s_time_t delta;
    uint64_t val;
    unsigned int credits;

    /* Assert svc is current */
    ASSERT( svc == CSCHED_VCPU(curr_on_cpu(svc->vcpu->processor)) );

    if ( (delta = now - svc->start_time) <= 0 )
        return;

    val = delta * CSCHED_CREDITS_PER_MSEC + svc->residual;
    svc->residual = do_div(val, MILLISECS(1));
    credits = val;
    ASSERT(credits == val); /* make sure we haven't truncated val */
    atomic_sub(credits, &svc->credit);
    svc->start_time += (credits * MILLISECS(1)) / CSCHED_CREDITS_PER_MSEC;
}

static bool_t __read_mostly opt_tickle_one_idle = 1;
boolean_param("tickle_one_idle_cpu", opt_tickle_one_idle);

DEFINE_PER_CPU(unsigned int, last_tickle_cpu);

static inline void
__runq_tickle(unsigned int cpu, struct csched_vcpu *new)
{
    struct csched_vcpu * const cur = CSCHED_VCPU(curr_on_cpu(cpu));
    struct csched_private *prv = CSCHED_PRIV(per_cpu(scheduler, cpu));
    cpumask_t mask, idle_mask;
    int balance_step, idlers_empty;

    ASSERT(cur);
    cpumask_clear(&mask);
    idlers_empty = cpumask_empty(prv->idlers);


    /*
     * If the pcpu is idle, or there are no idlers and the new
     * vcpu is a higher priority than the old vcpu, run it here.
     *
     * If there are idle cpus, first try to find one suitable to run
     * new, so we can avoid preempting cur.  If we cannot find a
     * suitable idler on which to run new, run it here, but try to
     * find a suitable idler on which to run cur instead.
     */
    if ( cur->pri == CSCHED_PRI_IDLE
         || (idlers_empty && new->pri > cur->pri) )
    {
        if ( cur->pri != CSCHED_PRI_IDLE )
            SCHED_STAT_CRANK(tickle_idlers_none);
        cpumask_set_cpu(cpu, &mask);
    }
    else if ( !idlers_empty )
    {
        /*
         * Node and vcpu-affinity balancing loop. For vcpus without
         * a useful node-affinity, consider vcpu-affinity only.
         */
        for_each_csched_balance_step( balance_step )
        {
            int new_idlers_empty;

            if ( balance_step == CSCHED_BALANCE_NODE_AFFINITY
                 && !__vcpu_has_node_affinity(new->vcpu) )
                continue;

            /* Are there idlers suitable for new (for this balance step)? */
            csched_balance_cpumask(new->vcpu, balance_step,
                                   csched_balance_mask);
            cpumask_and(&idle_mask, prv->idlers, csched_balance_mask);
            new_idlers_empty = cpumask_empty(&idle_mask);

            /*
             * Let's not be too harsh! If there aren't idlers suitable
             * for new in its node-affinity mask, make sure we check its
             * vcpu-affinity as well, before taking final decisions.
             */
            if ( new_idlers_empty
                 && balance_step == CSCHED_BALANCE_NODE_AFFINITY )
                continue;

            /*
             * If there are no suitable idlers for new, and it's higher
             * priority than cur, ask the scheduler to migrate cur away.
             * We have to act like this (instead of just waking some of
             * the idlers suitable for cur) because cur is running.
             *
             * If there are suitable idlers for new, no matter priorities,
             * leave cur alone (as it is running and is, likely, cache-hot)
             * and wake some of them (which is waking up and so is, likely,
             * cache cold anyway).
             */
            if ( new_idlers_empty && new->pri > cur->pri )
            {
                SCHED_STAT_CRANK(tickle_idlers_none);
                SCHED_VCPU_STAT_CRANK(cur, kicked_away);
                SCHED_VCPU_STAT_CRANK(cur, migrate_r);
                SCHED_STAT_CRANK(migrate_kicked_away);
                set_bit(_VPF_migrating, &cur->vcpu->pause_flags);
                cpumask_set_cpu(cpu, &mask);
            }
            else if ( !new_idlers_empty )
            {
                /* Which of the idlers suitable for new shall we wake up? */
                SCHED_STAT_CRANK(tickle_idlers_some);
                if ( opt_tickle_one_idle )
                {
                    this_cpu(last_tickle_cpu) =
                        cpumask_cycle(this_cpu(last_tickle_cpu), &idle_mask);
                    cpumask_set_cpu(this_cpu(last_tickle_cpu), &mask);
                }
                else
                    cpumask_or(&mask, &mask, &idle_mask);
            }

            /* Did we find anyone? */
            if ( !cpumask_empty(&mask) )
                break;
        }
    }

    if ( !cpumask_empty(&mask) )
    {
        if ( unlikely(tb_init_done) )
        {
            /* Avoid TRACE_*: saves checking !tb_init_done each step */
            for_each_cpu(cpu, &mask)
                __trace_var(TRC_CSCHED_TICKLE, 0, sizeof(cpu), &cpu);
        }

        /* Send scheduler interrupts to designated CPUs */
        cpumask_raise_softirq(&mask, SCHEDULE_SOFTIRQ);
    }
}

static void
csched_free_pdata(const struct scheduler *ops, void *pcpu, int cpu)
{
    struct csched_private *prv = CSCHED_PRIV(ops);
    struct csched_pcpu *spc = pcpu;
    unsigned long flags;

    if ( spc == NULL )
        return;

    spin_lock_irqsave(&prv->lock, flags);

    prv->credit -= prv->credits_per_tslice;
    prv->ncpus--;
    cpumask_clear_cpu(cpu, prv->idlers);
    cpumask_clear_cpu(cpu, prv->cpus);
    if ( (prv->master == cpu) && (prv->ncpus > 0) )
    {
        prv->master = cpumask_first(prv->cpus);
        migrate_timer(&prv->master_ticker, prv->master);
    }
    kill_timer(&spc->ticker);
    if ( prv->ncpus == 0 )
        kill_timer(&prv->master_ticker);

    spin_unlock_irqrestore(&prv->lock, flags);

    free_cpumask_var(spc->balance_mask);
    xfree(spc);
}

static void *
csched_alloc_pdata(const struct scheduler *ops, int cpu)
{
    struct csched_pcpu *spc;
    struct csched_private *prv = CSCHED_PRIV(ops);
    unsigned long flags;

    /* Allocate per-PCPU info */
    spc = xzalloc(struct csched_pcpu);
    if ( spc == NULL )
        return NULL;

    if ( !alloc_cpumask_var(&spc->balance_mask) )
    {
        xfree(spc);
        return NULL;
    }

    spin_lock_irqsave(&prv->lock, flags);

    /* Initialize/update system-wide config */
    prv->credit += prv->credits_per_tslice;
    prv->ncpus++;
    cpumask_set_cpu(cpu, prv->cpus);
    if ( prv->ncpus == 1 )
    {
        prv->master = cpu;
        init_timer(&prv->master_ticker, csched_acct, prv, cpu);
        set_timer(&prv->master_ticker,
                  NOW() + MILLISECS(prv->tslice_ms));
    }

    init_timer(&spc->ticker, csched_tick, (void *)(unsigned long)cpu, cpu);
    set_timer(&spc->ticker, NOW() + MICROSECS(prv->tick_period_us) );

    INIT_LIST_HEAD(&spc->runq);
    spc->runq_sort_last = prv->runq_sort;
    spc->idle_bias = nr_cpu_ids - 1;
    if ( per_cpu(schedule_data, cpu).sched_priv == NULL )
        per_cpu(schedule_data, cpu).sched_priv = spc;

    /* Start off idling... */
    BUG_ON(!is_idle_vcpu(curr_on_cpu(cpu)));
    cpumask_set_cpu(cpu, prv->idlers);

    spin_unlock_irqrestore(&prv->lock, flags);

    return spc;
}

#ifndef NDEBUG
static inline void
__csched_vcpu_check(struct vcpu *vc)
{
    struct csched_vcpu * const svc = CSCHED_VCPU(vc);
    struct csched_dom * const sdom = svc->sdom;

    BUG_ON( svc->vcpu != vc );
    BUG_ON( sdom != CSCHED_DOM(vc->domain) );
    if ( sdom )
    {
        BUG_ON( is_idle_vcpu(vc) );
        BUG_ON( sdom->dom != vc->domain );
    }
    else
    {
        BUG_ON( !is_idle_vcpu(vc) );
    }

    SCHED_STAT_CRANK(vcpu_check);
}
#define CSCHED_VCPU_CHECK(_vc)  (__csched_vcpu_check(_vc))
#else
#define CSCHED_VCPU_CHECK(_vc)
#endif

/*
 * Delay, in microseconds, between migrations of a VCPU between PCPUs.
 * This prevents rapid fluttering of a VCPU between CPUs, and reduces the
 * implicit overheads such as cache-warming. 1ms (1000) has been measured
 * as a good value.
 */
static unsigned int vcpu_migration_delay;
integer_param("vcpu_migration_delay", vcpu_migration_delay);

void set_vcpu_migration_delay(unsigned int delay)
{
    vcpu_migration_delay = delay;
}

unsigned int get_vcpu_migration_delay(void)
{
    return vcpu_migration_delay;
}

static inline int
__csched_vcpu_is_cache_hot(struct vcpu *v)
{
    int hot = ((NOW() - v->last_run_time) <
               ((uint64_t)vcpu_migration_delay * 1000u));

    if ( hot )
        SCHED_STAT_CRANK(vcpu_hot);

    return hot;
}

static inline int
__csched_vcpu_is_migrateable(struct vcpu *vc, int dest_cpu, cpumask_t *mask)
{
    /*
     * Don't pick up work that's in the peer's scheduling tail or hot on
     * peer PCPU. Only pick up work that prefers and/or is allowed to run
     * on our CPU.
     */
    return !vc->is_running &&
           !__csched_vcpu_is_cache_hot(vc) &&
           cpumask_test_cpu(dest_cpu, mask);
}

static int
_csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc, bool_t commit)
{
    cpumask_t cpus;
    cpumask_t idlers;
    cpumask_t *online;
    struct csched_pcpu *spc = NULL;
    int cpu = vc->processor;
    int balance_step;

    online = cpupool_scheduler_cpumask(vc->domain->cpupool);
    for_each_csched_balance_step( balance_step )
    {
        if ( balance_step == CSCHED_BALANCE_NODE_AFFINITY
             && !__vcpu_has_node_affinity(vc) )
            continue;

        /* Pick an online CPU from the proper affinity mask */
        csched_balance_cpumask(vc, balance_step, &cpus);
        cpumask_and(&cpus, &cpus, online);

        /* If present, prefer vc's current processor */
        cpu = cpumask_test_cpu(vc->processor, &cpus)
                ? vc->processor
                : cpumask_cycle(vc->processor, &cpus);
        ASSERT( !cpumask_empty(&cpus) && cpumask_test_cpu(cpu, &cpus) );

        /*
         * Try to find an idle processor within the above constraints.
         *
         * In multi-core and multi-threaded CPUs, not all idle execution
         * vehicles are equal!
         *
         * We give preference to the idle execution vehicle with the most
         * idling neighbours in its grouping. This distributes work across
         * distinct cores first and guarantees we don't do something stupid
         * like run two VCPUs on co-hyperthreads while there are idle cores
         * or sockets.
         *
         * Notice that, when computing the "idleness" of cpu, we may want to
         * discount vc. That is, iff vc is the currently running and the only
         * runnable vcpu on cpu, we add cpu to the idlers.
         */
        cpumask_and(&idlers, &cpu_online_map, CSCHED_PRIV(ops)->idlers);
        if ( vc->processor == cpu && IS_RUNQ_IDLE(cpu) )
            cpumask_set_cpu(cpu, &idlers);
        cpumask_and(&cpus, &cpus, &idlers);

        /*
         * It is important that cpu points to an idle processor, if a suitable
         * one exists (and we can use cpus to check and, possibly, choose a new
         * CPU, as we just &&-ed it with idlers). In fact, if we are on SMT, and
         * cpu points to a busy thread with an idle sibling, both the threads
         * will be considered the same, from the "idleness" calculation point
         * of view", preventing vcpu from being moved to the thread that is
         * actually idle.
         *
         * Notice that cpumask_test_cpu() is quicker than cpumask_empty(), so
         * we check for it first.
         */
        if ( !cpumask_test_cpu(cpu, &cpus) && !cpumask_empty(&cpus) )
            cpu = cpumask_cycle(cpu, &cpus);
        cpumask_clear_cpu(cpu, &cpus);

        while ( !cpumask_empty(&cpus) )
        {
            cpumask_t cpu_idlers;
            cpumask_t nxt_idlers;
            int nxt, weight_cpu, weight_nxt;
            int migrate_factor;

            nxt = cpumask_cycle(cpu, &cpus);

            if ( cpumask_test_cpu(cpu, per_cpu(cpu_core_mask, nxt)) )
            {
                /* We're on the same socket, so check the busy-ness of threads.
                 * Migrate if # of idlers is less at all */
                ASSERT( cpumask_test_cpu(nxt, per_cpu(cpu_core_mask, cpu)) );
                migrate_factor = 1;
                cpumask_and(&cpu_idlers, &idlers, per_cpu(cpu_sibling_mask,
                            cpu));
                cpumask_and(&nxt_idlers, &idlers, per_cpu(cpu_sibling_mask,
                            nxt));
            }
            else
            {
                /* We're on different sockets, so check the busy-ness of cores.
                 * Migrate only if the other core is twice as idle */
                ASSERT( !cpumask_test_cpu(nxt, per_cpu(cpu_core_mask, cpu)) );
                migrate_factor = 2;
                cpumask_and(&cpu_idlers, &idlers, per_cpu(cpu_core_mask, cpu));
                cpumask_and(&nxt_idlers, &idlers, per_cpu(cpu_core_mask, nxt));
            }

            weight_cpu = cpumask_weight(&cpu_idlers);
            weight_nxt = cpumask_weight(&nxt_idlers);
            /* smt_power_savings: consolidate work rather than spreading it */
            if ( sched_smt_power_savings ?
                 weight_cpu > weight_nxt :
                 weight_cpu * migrate_factor < weight_nxt )


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