MFV r346563:

[FreeBSD/FreeBSD.git] / sys / kern / subr_smp.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2001, John Baldwin <jhb@FreeBSD.org>.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * This module holds the global variables and machine independent functions
 * used for the kernel SMP support.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/proc.h>
#include <sys/bus.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/pcpu.h>
#include <sys/sched.h>
#include <sys/smp.h>
#include <sys/sysctl.h>

#include <machine/cpu.h>
#include <machine/smp.h>

#include "opt_sched.h"

#ifdef SMP
MALLOC_DEFINE(M_TOPO, "toponodes", "SMP topology data");

volatile cpuset_t stopped_cpus;
volatile cpuset_t started_cpus;
volatile cpuset_t suspended_cpus;
cpuset_t hlt_cpus_mask;
cpuset_t logical_cpus_mask;

void (*cpustop_restartfunc)(void);
#endif

static int sysctl_kern_smp_active(SYSCTL_HANDLER_ARGS);

/* This is used in modules that need to work in both SMP and UP. */
cpuset_t all_cpus;

int mp_ncpus;
/* export this for libkvm consumers. */
int mp_maxcpus = MAXCPU;

volatile int smp_started;
u_int mp_maxid;

static SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD|CTLFLAG_CAPRD, NULL,
    "Kernel SMP");

SYSCTL_INT(_kern_smp, OID_AUTO, maxid, CTLFLAG_RD|CTLFLAG_CAPRD, &mp_maxid, 0,
    "Max CPU ID.");

SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD|CTLFLAG_CAPRD, &mp_maxcpus,
    0, "Max number of CPUs that the system was compiled for.");

SYSCTL_PROC(_kern_smp, OID_AUTO, active, CTLFLAG_RD|CTLTYPE_INT|CTLFLAG_MPSAFE,
    NULL, 0, sysctl_kern_smp_active, "I",
    "Indicates system is running in SMP mode");

int smp_disabled = 0;   /* has smp been disabled? */
SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN|CTLFLAG_CAPRD,
    &smp_disabled, 0, "SMP has been disabled from the loader");

int smp_cpus = 1;       /* how many cpu's running */
SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD|CTLFLAG_CAPRD, &smp_cpus, 0,
    "Number of CPUs online");

int smp_threads_per_core = 1;   /* how many SMT threads are running per core */
SYSCTL_INT(_kern_smp, OID_AUTO, threads_per_core, CTLFLAG_RD|CTLFLAG_CAPRD,
    &smp_threads_per_core, 0, "Number of SMT threads online per core");

int mp_ncores = -1;     /* how many physical cores running */
SYSCTL_INT(_kern_smp, OID_AUTO, cores, CTLFLAG_RD|CTLFLAG_CAPRD, &mp_ncores, 0,
    "Number of CPUs online");

int smp_topology = 0;   /* Which topology we're using. */
SYSCTL_INT(_kern_smp, OID_AUTO, topology, CTLFLAG_RDTUN, &smp_topology, 0,
    "Topology override setting; 0 is default provided by hardware.");

#ifdef SMP
/* Enable forwarding of a signal to a process running on a different CPU */
static int forward_signal_enabled = 1;
SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
           &forward_signal_enabled, 0,
           "Forwarding of a signal to a process on a different CPU");

/* Variables needed for SMP rendezvous. */
static volatile int smp_rv_ncpus;
static void (*volatile smp_rv_setup_func)(void *arg);
static void (*volatile smp_rv_action_func)(void *arg);
static void (*volatile smp_rv_teardown_func)(void *arg);
static void *volatile smp_rv_func_arg;
static volatile int smp_rv_waiters[4];

/* 
 * Shared mutex to restrict busywaits between smp_rendezvous() and
 * smp(_targeted)_tlb_shootdown().  A deadlock occurs if both of these
 * functions trigger at once and cause multiple CPUs to busywait with
 * interrupts disabled. 
 */
struct mtx smp_ipi_mtx;

/*
 * Let the MD SMP code initialize mp_maxid very early if it can.
 */
static void
mp_setmaxid(void *dummy)
{

        cpu_mp_setmaxid();

        KASSERT(mp_ncpus >= 1, ("%s: CPU count < 1", __func__));
        KASSERT(mp_ncpus > 1 || mp_maxid == 0,
            ("%s: one CPU but mp_maxid is not zero", __func__));
        KASSERT(mp_maxid >= mp_ncpus - 1,
            ("%s: counters out of sync: max %d, count %d", __func__,
                mp_maxid, mp_ncpus));
}
SYSINIT(cpu_mp_setmaxid, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_setmaxid, NULL);

/*
 * Call the MD SMP initialization code.
 */
static void
mp_start(void *dummy)
{

        mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);

        /* Probe for MP hardware. */
        if (smp_disabled != 0 || cpu_mp_probe() == 0) {
                mp_ncores = 1;
                mp_ncpus = 1;
                CPU_SETOF(PCPU_GET(cpuid), &all_cpus);
                return;
        }

        cpu_mp_start();
        printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
            mp_ncpus);

        /* Provide a default for most architectures that don't have SMT/HTT. */
        if (mp_ncores < 0)
                mp_ncores = mp_ncpus;

        cpu_mp_announce();
}
SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL);

void
forward_signal(struct thread *td)
{
        int id;

        /*
         * signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
         * this thread, so all we need to do is poke it if it is currently
         * executing so that it executes ast().
         */
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        KASSERT(TD_IS_RUNNING(td),
            ("forward_signal: thread is not TDS_RUNNING"));

        CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);

        if (!smp_started || cold || panicstr)
                return;
        if (!forward_signal_enabled)
                return;

        /* No need to IPI ourself. */
        if (td == curthread)
                return;

        id = td->td_oncpu;
        if (id == NOCPU)
                return;
        ipi_cpu(id, IPI_AST);
}

/*
 * When called the executing CPU will send an IPI to all other CPUs
 *  requesting that they halt execution.
 *
 * Usually (but not necessarily) called with 'other_cpus' as its arg.
 *
 *  - Signals all CPUs in map to stop.
 *  - Waits for each to stop.
 *
 * Returns:
 *  -1: error
 *   0: NA
 *   1: ok
 *
 */
#if defined(__amd64__) || defined(__i386__)
#define X86     1
#else
#define X86     0
#endif
static int
generic_stop_cpus(cpuset_t map, u_int type)
{
#ifdef KTR
        char cpusetbuf[CPUSETBUFSIZ];
#endif
        static volatile u_int stopping_cpu = NOCPU;
        int i;
        volatile cpuset_t *cpus;

        KASSERT(
            type == IPI_STOP || type == IPI_STOP_HARD
#if X86
            || type == IPI_SUSPEND
#endif
            , ("%s: invalid stop type", __func__));

        if (!smp_started)
                return (0);

        CTR2(KTR_SMP, "stop_cpus(%s) with %u type",
            cpusetobj_strprint(cpusetbuf, &map), type);

#if X86
        /*
         * When suspending, ensure there are are no IPIs in progress.
         * IPIs that have been issued, but not yet delivered (e.g.
         * not pending on a vCPU when running under virtualization)
         * will be lost, violating FreeBSD's assumption of reliable
         * IPI delivery.
         */
        if (type == IPI_SUSPEND)
                mtx_lock_spin(&smp_ipi_mtx);
#endif

#if X86
        if (!nmi_is_broadcast || nmi_kdb_lock == 0) {
#endif
        if (stopping_cpu != PCPU_GET(cpuid))
                while (atomic_cmpset_int(&stopping_cpu, NOCPU,
                    PCPU_GET(cpuid)) == 0)
                        while (stopping_cpu != NOCPU)
                                cpu_spinwait(); /* spin */

        /* send the stop IPI to all CPUs in map */
        ipi_selected(map, type);
#if X86
        }
#endif

#if X86
        if (type == IPI_SUSPEND)
                cpus = &suspended_cpus;
        else
#endif
                cpus = &stopped_cpus;

        i = 0;
        while (!CPU_SUBSET(cpus, &map)) {
                /* spin */
                cpu_spinwait();
                i++;
                if (i == 100000000) {
                        printf("timeout stopping cpus\n");
                        break;
                }
        }

#if X86
        if (type == IPI_SUSPEND)
                mtx_unlock_spin(&smp_ipi_mtx);
#endif

        stopping_cpu = NOCPU;
        return (1);
}

int
stop_cpus(cpuset_t map)
{

        return (generic_stop_cpus(map, IPI_STOP));
}

int
stop_cpus_hard(cpuset_t map)
{

        return (generic_stop_cpus(map, IPI_STOP_HARD));
}

#if X86
int
suspend_cpus(cpuset_t map)
{

        return (generic_stop_cpus(map, IPI_SUSPEND));
}
#endif

/*
 * Called by a CPU to restart stopped CPUs. 
 *
 * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
 *
 *  - Signals all CPUs in map to restart.
 *  - Waits for each to restart.
 *
 * Returns:
 *  -1: error
 *   0: NA
 *   1: ok
 */
static int
generic_restart_cpus(cpuset_t map, u_int type)
{
#ifdef KTR
        char cpusetbuf[CPUSETBUFSIZ];
#endif
        volatile cpuset_t *cpus;

        KASSERT(type == IPI_STOP || type == IPI_STOP_HARD
#if X86
            || type == IPI_SUSPEND
#endif
            , ("%s: invalid stop type", __func__));

        if (!smp_started)
                return (0);

        CTR1(KTR_SMP, "restart_cpus(%s)", cpusetobj_strprint(cpusetbuf, &map));

#if X86
        if (type == IPI_SUSPEND)
                cpus = &resuming_cpus;
        else
#endif
                cpus = &stopped_cpus;

        /* signal other cpus to restart */
#if X86
        if (type == IPI_SUSPEND)
                CPU_COPY_STORE_REL(&map, &toresume_cpus);
        else
#endif
                CPU_COPY_STORE_REL(&map, &started_cpus);

#if X86
        if (!nmi_is_broadcast || nmi_kdb_lock == 0) {
#endif
        /* wait for each to clear its bit */
        while (CPU_OVERLAP(cpus, &map))
                cpu_spinwait();
#if X86
        }
#endif

        return (1);
}

int
restart_cpus(cpuset_t map)
{

        return (generic_restart_cpus(map, IPI_STOP));
}

#if X86
int
resume_cpus(cpuset_t map)
{

        return (generic_restart_cpus(map, IPI_SUSPEND));
}
#endif
#undef X86

/*
 * All-CPU rendezvous.  CPUs are signalled, all execute the setup function 
 * (if specified), rendezvous, execute the action function (if specified),
 * rendezvous again, execute the teardown function (if specified), and then
 * resume.
 *
 * Note that the supplied external functions _must_ be reentrant and aware
 * that they are running in parallel and in an unknown lock context.
 */
void
smp_rendezvous_action(void)
{
        struct thread *td;
        void *local_func_arg;
        void (*local_setup_func)(void*);
        void (*local_action_func)(void*);
        void (*local_teardown_func)(void*);
#ifdef INVARIANTS
        int owepreempt;
#endif

        /* Ensure we have up-to-date values. */
        atomic_add_acq_int(&smp_rv_waiters[0], 1);
        while (smp_rv_waiters[0] < smp_rv_ncpus)
                cpu_spinwait();

        /* Fetch rendezvous parameters after acquire barrier. */
        local_func_arg = smp_rv_func_arg;
        local_setup_func = smp_rv_setup_func;
        local_action_func = smp_rv_action_func;
        local_teardown_func = smp_rv_teardown_func;

        /*
         * Use a nested critical section to prevent any preemptions
         * from occurring during a rendezvous action routine.
         * Specifically, if a rendezvous handler is invoked via an IPI
         * and the interrupted thread was in the critical_exit()
         * function after setting td_critnest to 0 but before
         * performing a deferred preemption, this routine can be
         * invoked with td_critnest set to 0 and td_owepreempt true.
         * In that case, a critical_exit() during the rendezvous
         * action would trigger a preemption which is not permitted in
         * a rendezvous action.  To fix this, wrap all of the
         * rendezvous action handlers in a critical section.  We
         * cannot use a regular critical section however as having
         * critical_exit() preempt from this routine would also be
         * problematic (the preemption must not occur before the IPI
         * has been acknowledged via an EOI).  Instead, we
         * intentionally ignore td_owepreempt when leaving the
         * critical section.  This should be harmless because we do
         * not permit rendezvous action routines to schedule threads,
         * and thus td_owepreempt should never transition from 0 to 1
         * during this routine.
         */
        td = curthread;
        td->td_critnest++;
#ifdef INVARIANTS
        owepreempt = td->td_owepreempt;
#endif
        
        /*
         * If requested, run a setup function before the main action
         * function.  Ensure all CPUs have completed the setup
         * function before moving on to the action function.
         */
        if (local_setup_func != smp_no_rendezvous_barrier) {
                if (smp_rv_setup_func != NULL)
                        smp_rv_setup_func(smp_rv_func_arg);
                atomic_add_int(&smp_rv_waiters[1], 1);
                while (smp_rv_waiters[1] < smp_rv_ncpus)
                        cpu_spinwait();
        }

        if (local_action_func != NULL)
                local_action_func(local_func_arg);

        if (local_teardown_func != smp_no_rendezvous_barrier) {
                /*
                 * Signal that the main action has been completed.  If a
                 * full exit rendezvous is requested, then all CPUs will
                 * wait here until all CPUs have finished the main action.
                 */
                atomic_add_int(&smp_rv_waiters[2], 1);
                while (smp_rv_waiters[2] < smp_rv_ncpus)
                        cpu_spinwait();

                if (local_teardown_func != NULL)
                        local_teardown_func(local_func_arg);
        }

        /*
         * Signal that the rendezvous is fully completed by this CPU.
         * This means that no member of smp_rv_* pseudo-structure will be
         * accessed by this target CPU after this point; in particular,
         * memory pointed by smp_rv_func_arg.
         *
         * The release semantic ensures that all accesses performed by
         * the current CPU are visible when smp_rendezvous_cpus()
         * returns, by synchronizing with the
         * atomic_load_acq_int(&smp_rv_waiters[3]).
         */
        atomic_add_rel_int(&smp_rv_waiters[3], 1);

        td->td_critnest--;
        KASSERT(owepreempt == td->td_owepreempt,
            ("rendezvous action changed td_owepreempt"));
}

void
smp_rendezvous_cpus(cpuset_t map,
        void (* setup_func)(void *), 
        void (* action_func)(void *),
        void (* teardown_func)(void *),
        void *arg)
{
        int curcpumap, i, ncpus = 0;

        /* Look comments in the !SMP case. */
        if (!smp_started) {
                spinlock_enter();
                if (setup_func != NULL)
                        setup_func(arg);
                if (action_func != NULL)
                        action_func(arg);
                if (teardown_func != NULL)
                        teardown_func(arg);
                spinlock_exit();
                return;
        }

        CPU_FOREACH(i) {
                if (CPU_ISSET(i, &map))
                        ncpus++;
        }
        if (ncpus == 0)
                panic("ncpus is 0 with non-zero map");

        mtx_lock_spin(&smp_ipi_mtx);

        /* Pass rendezvous parameters via global variables. */
        smp_rv_ncpus = ncpus;
        smp_rv_setup_func = setup_func;
        smp_rv_action_func = action_func;
        smp_rv_teardown_func = teardown_func;
        smp_rv_func_arg = arg;
        smp_rv_waiters[1] = 0;
        smp_rv_waiters[2] = 0;
        smp_rv_waiters[3] = 0;
        atomic_store_rel_int(&smp_rv_waiters[0], 0);

        /*
         * Signal other processors, which will enter the IPI with
         * interrupts off.
         */
        curcpumap = CPU_ISSET(curcpu, &map);
        CPU_CLR(curcpu, &map);
        ipi_selected(map, IPI_RENDEZVOUS);

        /* Check if the current CPU is in the map */
        if (curcpumap != 0)
                smp_rendezvous_action();

        /*
         * Ensure that the master CPU waits for all the other
         * CPUs to finish the rendezvous, so that smp_rv_*
         * pseudo-structure and the arg are guaranteed to not
         * be in use.
         *
         * Load acquire synchronizes with the release add in
         * smp_rendezvous_action(), which ensures that our caller sees
         * all memory actions done by the called functions on other
         * CPUs.
         */
        while (atomic_load_acq_int(&smp_rv_waiters[3]) < ncpus)
                cpu_spinwait();

        mtx_unlock_spin(&smp_ipi_mtx);
}

void
smp_rendezvous(void (* setup_func)(void *), 
               void (* action_func)(void *),
               void (* teardown_func)(void *),
               void *arg)
{
        smp_rendezvous_cpus(all_cpus, setup_func, action_func, teardown_func, arg);
}

static struct cpu_group group[MAXCPU * MAX_CACHE_LEVELS + 1];

struct cpu_group *
smp_topo(void)
{
        char cpusetbuf[CPUSETBUFSIZ], cpusetbuf2[CPUSETBUFSIZ];
        struct cpu_group *top;

        /*
         * Check for a fake topology request for debugging purposes.
         */
        switch (smp_topology) {
        case 1:
                /* Dual core with no sharing.  */
                top = smp_topo_1level(CG_SHARE_NONE, 2, 0);
                break;
        case 2:
                /* No topology, all cpus are equal. */
                top = smp_topo_none();
                break;
        case 3:
                /* Dual core with shared L2.  */
                top = smp_topo_1level(CG_SHARE_L2, 2, 0);
                break;
        case 4:
                /* quad core, shared l3 among each package, private l2.  */
                top = smp_topo_1level(CG_SHARE_L3, 4, 0);
                break;
        case 5:
                /* quad core,  2 dualcore parts on each package share l2.  */
                top = smp_topo_2level(CG_SHARE_NONE, 2, CG_SHARE_L2, 2, 0);
                break;
        case 6:
                /* Single-core 2xHTT */
                top = smp_topo_1level(CG_SHARE_L1, 2, CG_FLAG_HTT);
                break;
        case 7:
                /* quad core with a shared l3, 8 threads sharing L2.  */
                top = smp_topo_2level(CG_SHARE_L3, 4, CG_SHARE_L2, 8,
                    CG_FLAG_SMT);
                break;
        default:
                /* Default, ask the system what it wants. */
                top = cpu_topo();
                break;
        }
        /*
         * Verify the returned topology.
         */
        if (top->cg_count != mp_ncpus)
                panic("Built bad topology at %p.  CPU count %d != %d",
                    top, top->cg_count, mp_ncpus);
        if (CPU_CMP(&top->cg_mask, &all_cpus))
                panic("Built bad topology at %p.  CPU mask (%s) != (%s)",
                    top, cpusetobj_strprint(cpusetbuf, &top->cg_mask),
                    cpusetobj_strprint(cpusetbuf2, &all_cpus));

        /*
         * Collapse nonsense levels that may be created out of convenience by
         * the MD layers.  They cause extra work in the search functions.
         */
        while (top->cg_children == 1) {
                top = &top->cg_child[0];
                top->cg_parent = NULL;
        }
        return (top);
}

struct cpu_group *
smp_topo_alloc(u_int count)
{
        static u_int index;
        u_int curr;

        curr = index;
        index += count;
        return (&group[curr]);
}

struct cpu_group *
smp_topo_none(void)
{
        struct cpu_group *top;

        top = &group[0];
        top->cg_parent = NULL;
        top->cg_child = NULL;
        top->cg_mask = all_cpus;
        top->cg_count = mp_ncpus;
        top->cg_children = 0;
        top->cg_level = CG_SHARE_NONE;
        top->cg_flags = 0;
        
        return (top);
}

static int
smp_topo_addleaf(struct cpu_group *parent, struct cpu_group *child, int share,
    int count, int flags, int start)
{
        char cpusetbuf[CPUSETBUFSIZ], cpusetbuf2[CPUSETBUFSIZ];
        cpuset_t mask;
        int i;

        CPU_ZERO(&mask);
        for (i = 0; i < count; i++, start++)
                CPU_SET(start, &mask);
        child->cg_parent = parent;
        child->cg_child = NULL;
        child->cg_children = 0;
        child->cg_level = share;
        child->cg_count = count;
        child->cg_flags = flags;
        child->cg_mask = mask;
        parent->cg_children++;
        for (; parent != NULL; parent = parent->cg_parent) {
                if (CPU_OVERLAP(&parent->cg_mask, &child->cg_mask))
                        panic("Duplicate children in %p.  mask (%s) child (%s)",
                            parent,
                            cpusetobj_strprint(cpusetbuf, &parent->cg_mask),
                            cpusetobj_strprint(cpusetbuf2, &child->cg_mask));
                CPU_OR(&parent->cg_mask, &child->cg_mask);
                parent->cg_count += child->cg_count;
        }

        return (start);
}

struct cpu_group *
smp_topo_1level(int share, int count, int flags)
{
        struct cpu_group *child;
        struct cpu_group *top;
        int packages;
        int cpu;
        int i;

        cpu = 0;
        top = &group[0];
        packages = mp_ncpus / count;
        top->cg_child = child = &group[1];
        top->cg_level = CG_SHARE_NONE;
        for (i = 0; i < packages; i++, child++)
                cpu = smp_topo_addleaf(top, child, share, count, flags, cpu);
        return (top);
}

struct cpu_group *
smp_topo_2level(int l2share, int l2count, int l1share, int l1count,
    int l1flags)
{
        struct cpu_group *top;
        struct cpu_group *l1g;
        struct cpu_group *l2g;
        int cpu;
        int i;
        int j;

        cpu = 0;
        top = &group[0];
        l2g = &group[1];
        top->cg_child = l2g;
        top->cg_level = CG_SHARE_NONE;
        top->cg_children = mp_ncpus / (l2count * l1count);
        l1g = l2g + top->cg_children;
        for (i = 0; i < top->cg_children; i++, l2g++) {
                l2g->cg_parent = top;
                l2g->cg_child = l1g;
                l2g->cg_level = l2share;
                for (j = 0; j < l2count; j++, l1g++)
                        cpu = smp_topo_addleaf(l2g, l1g, l1share, l1count,
                            l1flags, cpu);
        }
        return (top);
}


struct cpu_group *
smp_topo_find(struct cpu_group *top, int cpu)
{
        struct cpu_group *cg;
        cpuset_t mask;
        int children;
        int i;

        CPU_SETOF(cpu, &mask);
        cg = top;
        for (;;) {
                if (!CPU_OVERLAP(&cg->cg_mask, &mask))
                        return (NULL);
                if (cg->cg_children == 0)
                        return (cg);
                children = cg->cg_children;
                for (i = 0, cg = cg->cg_child; i < children; cg++, i++)
                        if (CPU_OVERLAP(&cg->cg_mask, &mask))
                                break;
        }
        return (NULL);
}
#else /* !SMP */

void
smp_rendezvous_cpus(cpuset_t map,
        void (*setup_func)(void *), 
        void (*action_func)(void *),
        void (*teardown_func)(void *),
        void *arg)
{
        /*
         * In the !SMP case we just need to ensure the same initial conditions
         * as the SMP case.
         */
        spinlock_enter();
        if (setup_func != NULL)
                setup_func(arg);
        if (action_func != NULL)
                action_func(arg);
        if (teardown_func != NULL)
                teardown_func(arg);
        spinlock_exit();
}

void
smp_rendezvous(void (*setup_func)(void *), 
               void (*action_func)(void *),
               void (*teardown_func)(void *),
               void *arg)
{

        smp_rendezvous_cpus(all_cpus, setup_func, action_func, teardown_func,
            arg);
}

/*
 * Provide dummy SMP support for UP kernels.  Modules that need to use SMP
 * APIs will still work using this dummy support.
 */
static void
mp_setvariables_for_up(void *dummy)
{
        mp_ncpus = 1;
        mp_ncores = 1;
        mp_maxid = PCPU_GET(cpuid);
        CPU_SETOF(mp_maxid, &all_cpus);
        KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
}
SYSINIT(cpu_mp_setvariables, SI_SUB_TUNABLES, SI_ORDER_FIRST,
    mp_setvariables_for_up, NULL);
#endif /* SMP */

void
smp_no_rendezvous_barrier(void *dummy)
{
#ifdef SMP
        KASSERT((!smp_started),("smp_no_rendezvous called and smp is started"));
#endif
}

/*
 * Wait for specified idle threads to switch once.  This ensures that even
 * preempted threads have cycled through the switch function once,
 * exiting their codepaths.  This allows us to change global pointers
 * with no other synchronization.
 */
int
quiesce_cpus(cpuset_t map, const char *wmesg, int prio)
{
        struct pcpu *pcpu;
        u_int gen[MAXCPU];
        int error;
        int cpu;

        error = 0;
        for (cpu = 0; cpu <= mp_maxid; cpu++) {
                if (!CPU_ISSET(cpu, &map) || CPU_ABSENT(cpu))
                        continue;
                pcpu = pcpu_find(cpu);
                gen[cpu] = pcpu->pc_idlethread->td_generation;
        }
        for (cpu = 0; cpu <= mp_maxid; cpu++) {
                if (!CPU_ISSET(cpu, &map) || CPU_ABSENT(cpu))
                        continue;
                pcpu = pcpu_find(cpu);
                thread_lock(curthread);
                sched_bind(curthread, cpu);
                thread_unlock(curthread);
                while (gen[cpu] == pcpu->pc_idlethread->td_generation) {
                        error = tsleep(quiesce_cpus, prio, wmesg, 1);
                        if (error != EWOULDBLOCK)
                                goto out;
                        error = 0;
                }
        }
out:
        thread_lock(curthread);
        sched_unbind(curthread);
        thread_unlock(curthread);

        return (error);
}

int
quiesce_all_cpus(const char *wmesg, int prio)
{

        return quiesce_cpus(all_cpus, wmesg, prio);
}

/* Extra care is taken with this sysctl because the data type is volatile */
static int
sysctl_kern_smp_active(SYSCTL_HANDLER_ARGS)
{
        int error, active;

        active = smp_started;
        error = SYSCTL_OUT(req, &active, sizeof(active));
        return (error);
}


#ifdef SMP
void
topo_init_node(struct topo_node *node)
{

        bzero(node, sizeof(*node));
        TAILQ_INIT(&node->children);
}

void
topo_init_root(struct topo_node *root)
{

        topo_init_node(root);
        root->type = TOPO_TYPE_SYSTEM;
}

/*
 * Add a child node with the given ID under the given parent.
 * Do nothing if there is already a child with that ID.
 */
struct topo_node *
topo_add_node_by_hwid(struct topo_node *parent, int hwid,
    topo_node_type type, uintptr_t subtype)
{
        struct topo_node *node;

        TAILQ_FOREACH_REVERSE(node, &parent->children,
            topo_children, siblings) {
                if (node->hwid == hwid
                    && node->type == type && node->subtype == subtype) {
                        return (node);
                }
        }

        node = malloc(sizeof(*node), M_TOPO, M_WAITOK);
        topo_init_node(node);
        node->parent = parent;
        node->hwid = hwid;
        node->type = type;
        node->subtype = subtype;
        TAILQ_INSERT_TAIL(&parent->children, node, siblings);
        parent->nchildren++;

        return (node);
}

/*
 * Find a child node with the given ID under the given parent.
 */
struct topo_node *
topo_find_node_by_hwid(struct topo_node *parent, int hwid,
    topo_node_type type, uintptr_t subtype)
{

        struct topo_node *node;

        TAILQ_FOREACH(node, &parent->children, siblings) {
                if (node->hwid == hwid
                    && node->type == type && node->subtype == subtype) {
                        return (node);
                }
        }

        return (NULL);
}

/*
 * Given a node change the order of its parent's child nodes such
 * that the node becomes the firt child while preserving the cyclic
 * order of the children.  In other words, the given node is promoted
 * by rotation.
 */
void
topo_promote_child(struct topo_node *child)
{
        struct topo_node *next;
        struct topo_node *node;
        struct topo_node *parent;

        parent = child->parent;
        next = TAILQ_NEXT(child, siblings);
        TAILQ_REMOVE(&parent->children, child, siblings);
        TAILQ_INSERT_HEAD(&parent->children, child, siblings);

        while (next != NULL) {
                node = next;
                next = TAILQ_NEXT(node, siblings);
                TAILQ_REMOVE(&parent->children, node, siblings);
                TAILQ_INSERT_AFTER(&parent->children, child, node, siblings);
                child = node;
        }
}

/*
 * Iterate to the next node in the depth-first search (traversal) of
 * the topology tree.
 */
struct topo_node *
topo_next_node(struct topo_node *top, struct topo_node *node)
{
        struct topo_node *next;

        if ((next = TAILQ_FIRST(&node->children)) != NULL)
                return (next);

        if ((next = TAILQ_NEXT(node, siblings)) != NULL)
                return (next);

        while (node != top && (node = node->parent) != top)
                if ((next = TAILQ_NEXT(node, siblings)) != NULL)
                        return (next);

        return (NULL);
}

/*
 * Iterate to the next node in the depth-first search of the topology tree,
 * but without descending below the current node.
 */
struct topo_node *
topo_next_nonchild_node(struct topo_node *top, struct topo_node *node)
{
        struct topo_node *next;

        if ((next = TAILQ_NEXT(node, siblings)) != NULL)
                return (next);

        while (node != top && (node = node->parent) != top)
                if ((next = TAILQ_NEXT(node, siblings)) != NULL)
                        return (next);

        return (NULL);
}

/*
 * Assign the given ID to the given topology node that represents a logical
 * processor.
 */
void
topo_set_pu_id(struct topo_node *node, cpuid_t id)
{

        KASSERT(node->type == TOPO_TYPE_PU,
            ("topo_set_pu_id: wrong node type: %u", node->type));
        KASSERT(CPU_EMPTY(&node->cpuset) && node->cpu_count == 0,
            ("topo_set_pu_id: cpuset already not empty"));
        node->id = id;
        CPU_SET(id, &node->cpuset);
        node->cpu_count = 1;
        node->subtype = 1;

        while ((node = node->parent) != NULL) {
                KASSERT(!CPU_ISSET(id, &node->cpuset),
                    ("logical ID %u is already set in node %p", id, node));
                CPU_SET(id, &node->cpuset);
                node->cpu_count++;
        }
}

static struct topology_spec {
        topo_node_type  type;
        bool            match_subtype;
        uintptr_t       subtype;
} topology_level_table[TOPO_LEVEL_COUNT] = {
        [TOPO_LEVEL_PKG] = { .type = TOPO_TYPE_PKG, },
        [TOPO_LEVEL_GROUP] = { .type = TOPO_TYPE_GROUP, },
        [TOPO_LEVEL_CACHEGROUP] = {
                .type = TOPO_TYPE_CACHE,
                .match_subtype = true,
                .subtype = CG_SHARE_L3,
        },
        [TOPO_LEVEL_CORE] = { .type = TOPO_TYPE_CORE, },
        [TOPO_LEVEL_THREAD] = { .type = TOPO_TYPE_PU, },
};

static bool
topo_analyze_table(struct topo_node *root, int all, enum topo_level level,
    struct topo_analysis *results)
{
        struct topology_spec *spec;
        struct topo_node *node;
        int count;

        if (level >= TOPO_LEVEL_COUNT)
                return (true);

        spec = &topology_level_table[level];
        count = 0;
        node = topo_next_node(root, root);

        while (node != NULL) {
                if (node->type != spec->type ||
                    (spec->match_subtype && node->subtype != spec->subtype)) {
                        node = topo_next_node(root, node);
                        continue;
                }
                if (!all && CPU_EMPTY(&node->cpuset)) {
                        node = topo_next_nonchild_node(root, node);
                        continue;
                }

                count++;

                if (!topo_analyze_table(node, all, level + 1, results))
                        return (false);

                node = topo_next_nonchild_node(root, node);
        }

        /* No explicit subgroups is essentially one subgroup. */
        if (count == 0) {
                count = 1;

                if (!topo_analyze_table(root, all, level + 1, results))
                        return (false);
        }

        if (results->entities[level] == -1)
                results->entities[level] = count;
        else if (results->entities[level] != count)
                return (false);

        return (true);
}

/*
 * Check if the topology is uniform, that is, each package has the same number
 * of cores in it and each core has the same number of threads (logical
 * processors) in it.  If so, calculate the number of packages, the number of
 * groups per package, the number of cachegroups per group, and the number of
 * logical processors per cachegroup.  'all' parameter tells whether to include
 * administratively disabled logical processors into the analysis.
 */
int
topo_analyze(struct topo_node *topo_root, int all,
    struct topo_analysis *results)
{

        results->entities[TOPO_LEVEL_PKG] = -1;
        results->entities[TOPO_LEVEL_CORE] = -1;
        results->entities[TOPO_LEVEL_THREAD] = -1;
        results->entities[TOPO_LEVEL_GROUP] = -1;
        results->entities[TOPO_LEVEL_CACHEGROUP] = -1;

        if (!topo_analyze_table(topo_root, all, TOPO_LEVEL_PKG, results))
                return (0);

        KASSERT(results->entities[TOPO_LEVEL_PKG] > 0,
                ("bug in topology or analysis"));

        return (1);
}

#endif /* SMP */