FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_smp.c

     /*-
      * Copyright (c) 2001, John Baldwin <jhb@FreeBSD.org>.
      * All rights reserved.
      *
      * 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.
     * 3. Neither the name of the author nor the names of any co-contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * 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/mutex.h>
    #include <sys/pcpu.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    
    #include <machine/cpu.h>
    #include <machine/smp.h>
    
    #include "opt_sched.h"
    
    #ifdef SMP
    volatile cpumask_t stopped_cpus;
    volatile cpumask_t started_cpus;
    cpumask_t idle_cpus_mask;
    cpumask_t hlt_cpus_mask;
    cpumask_t logical_cpus_mask;
    
    void (*cpustop_restartfunc)(void);
    #endif
    /* This is used in modules that need to work in both SMP and UP. */
    cpumask_t all_cpus;
    
    int mp_ncpus;
    /* export this for libkvm consumers. */
    int mp_maxcpus = MAXCPU;
    
    struct cpu_top *smp_topology;
    volatile int smp_started;
    u_int mp_maxid;
    
    SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");
    
    SYSCTL_INT(_kern_smp, OID_AUTO, maxid, CTLFLAG_RD, &mp_maxid, 0,
        "Max CPU ID.");
    
    SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD, &mp_maxcpus, 0,
        "Max number of CPUs that the system was compiled for.");
    
    int smp_active = 0;     /* are the APs allowed to run? */
    SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0,
        "Number of Auxillary Processors (APs) that were successfully started");
    
    int smp_disabled = 0;   /* has smp been disabled? */
    SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN, &smp_disabled, 0,
        "SMP has been disabled from the loader");
    TUNABLE_INT("kern.smp.disabled", &smp_disabled);
    
    int smp_cpus = 1;       /* how many cpu's running */
    SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0,
        "Number of CPUs online");
    
    #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");
   
   /* Enable forwarding of roundrobin to all other cpus */
   static int forward_roundrobin_enabled = 1;
   SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
              &forward_roundrobin_enabled, 0,
              "Forwarding of roundrobin to all other CPUs");
   
   /* 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();
   }
   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)
   {
   
           /* Probe for MP hardware. */
           if (smp_disabled != 0 || cpu_mp_probe() == 0) {
                   mp_ncpus = 1;
                   all_cpus = PCPU_GET(cpumask);
                   return;
           }
   
           mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);
           cpu_mp_start();
           printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
               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_selected(1 << id, IPI_AST);
   }
   
   void
   forward_roundrobin(void)
   {
           struct pcpu *pc;
           struct thread *td;
           cpumask_t id, map, me;
   
           CTR0(KTR_SMP, "forward_roundrobin()");
   
           if (!smp_started || cold || panicstr)
                   return;
           if (!forward_roundrobin_enabled)
                   return;
           map = 0;
           me = PCPU_GET(cpumask);
           SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
                   td = pc->pc_curthread;
                   id = pc->pc_cpumask;
                   if (id != me && (id & stopped_cpus) == 0 &&
                       !TD_IS_IDLETHREAD(td)) {
                           td->td_flags |= TDF_NEEDRESCHED;
                           map |= id;
                   }
           }
           ipi_selected(map, 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
    *
    * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
    *            from executing at same time.
    */
   int
   stop_cpus(cpumask_t map)
   {
           int i;
   
           if (!smp_started)
                   return 0;
   
           CTR1(KTR_SMP, "stop_cpus(%x)", map);
   
           /* send the stop IPI to all CPUs in map */
           ipi_selected(map, IPI_STOP);
   
           i = 0;
           while ((stopped_cpus & map) != map) {
                   /* spin */
                   cpu_spinwait();
                   i++;
   #ifdef DIAGNOSTIC
                   if (i == 100000) {
                           printf("timeout stopping cpus\n");
                           break;
                   }
   #endif
           }
   
           return 1;
   }
   
   /*
    * 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
    */
   int
   restart_cpus(cpumask_t map)
   {
   
           if (!smp_started)
                   return 0;
   
           CTR1(KTR_SMP, "restart_cpus(%x)", map);
   
           /* signal other cpus to restart */
           atomic_store_rel_int(&started_cpus, map);
   
           /* wait for each to clear its bit */
           while ((stopped_cpus & map) != 0)
                   cpu_spinwait();
   
           return 1;
   }
   
   /*
    * 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 acknowleged via an EOI).  Instead, we
            * intentionally ignore td_owepreempt when leaving the
            * critical setion.  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_rendevous_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_rendevous_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.
            */
           atomic_add_int(&smp_rv_waiters[3], 1);
   
           td->td_critnest--;
           KASSERT(owepreempt == td->td_owepreempt,
               ("rendezvous action changed td_owepreempt"));
   }
   
   void
   smp_rendezvous_cpus(cpumask_t map,
           void (* setup_func)(void *), 
           void (* action_func)(void *),
           void (* teardown_func)(void *),
           void *arg)
   {
           int i, ncpus = 0;
   
           if (!smp_started) {
                   if (setup_func != NULL)
                           setup_func(arg);
                   if (action_func != NULL)
                           action_func(arg);
                   if (teardown_func != NULL)
                           teardown_func(arg);
                   return;
           }
   
           for (i = 0; i <= mp_maxid; i++)
                   if (((1 << i) & map) != 0 && !CPU_ABSENT(i))
                           ncpus++;
           if (ncpus == 0)
                   panic("ncpus is 0 with map=0x%x", 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.
            */
           ipi_selected(map & ~(1 << curcpu), IPI_RENDEZVOUS);
   
           /* Check if the current CPU is in the map */
           if ((map & (1 << curcpu)) != 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.
            */
           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);
   }
   #else /* !SMP */
   
   /*
    * 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_maxid = PCPU_GET(cpuid);
           all_cpus = PCPU_GET(cpumask);
           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);
   
   void
   smp_rendezvous_cpus(cpumask_t map,
           void (*setup_func)(void *), 
           void (*action_func)(void *),
           void (*teardown_func)(void *),
           void *arg)
   {
           if (setup_func != NULL)
                   setup_func(arg);
           if (action_func != NULL)
                   action_func(arg);
           if (teardown_func != NULL)
                   teardown_func(arg);
   }
   
   void
   smp_rendezvous(void (*setup_func)(void *), 
                  void (*action_func)(void *),
                  void (*teardown_func)(void *),
                  void *arg)
   {
   
           if (setup_func != NULL)
                   setup_func(arg);
           if (action_func != NULL)
                   action_func(arg);
           if (teardown_func != NULL)
                   teardown_func(arg);
   }
   #endif /* SMP */
   
   void
   smp_no_rendevous_barrier(void *dummy)
   {
   #ifdef SMP
           KASSERT((!smp_started),("smp_no_rendevous called and smp is started"));
   #endif
   }

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