The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * Copyright (c) 2001
    3  *      John Baldwin <jhb@FreeBSD.org>.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 4. Neither the name of the author nor the names of any co-contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY JOHN BALDWIN AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL JOHN BALDWIN OR THE VOICES IN HIS HEAD
   21  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   22  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   23  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   24  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   25  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   26  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
   27  * THE POSSIBILITY OF SUCH DAMAGE.
   28  */
   29 
   30 /*
   31  * This module holds the global variables and machine independent functions
   32  * used for the kernel SMP support.
   33  */
   34 
   35 #include <sys/cdefs.h>
   36 __FBSDID("$FreeBSD$");
   37 
   38 #include <sys/param.h>
   39 #include <sys/systm.h>
   40 #include <sys/kernel.h>
   41 #include <sys/ktr.h>
   42 #include <sys/proc.h>
   43 #include <sys/bus.h>
   44 #include <sys/lock.h>
   45 #include <sys/mutex.h>
   46 #include <sys/pcpu.h>
   47 #include <sys/smp.h>
   48 #include <sys/sysctl.h>
   49 
   50 #include <machine/cpu.h>
   51 #include <machine/smp.h>
   52 
   53 #include "opt_sched.h"
   54 
   55 #ifdef SMP
   56 volatile cpumask_t stopped_cpus;
   57 volatile cpumask_t started_cpus;
   58 cpumask_t idle_cpus_mask;
   59 cpumask_t hlt_cpus_mask;
   60 cpumask_t logical_cpus_mask;
   61 
   62 void (*cpustop_restartfunc)(void);
   63 #endif
   64 /* This is used in modules that need to work in both SMP and UP. */
   65 cpumask_t all_cpus;
   66 
   67 int mp_ncpus;
   68 /* export this for libkvm consumers. */
   69 int mp_maxcpus = MAXCPU;
   70 
   71 struct cpu_top *smp_topology;
   72 volatile int smp_started;
   73 u_int mp_maxid;
   74 
   75 SYSCTL_NODE(_kern, OID_AUTO, smp, CTLFLAG_RD, NULL, "Kernel SMP");
   76 
   77 SYSCTL_INT(_kern_smp, OID_AUTO, maxcpus, CTLFLAG_RD, &mp_maxcpus, 0,
   78     "Max number of CPUs that the system was compiled for.");
   79 
   80 int smp_active = 0;     /* are the APs allowed to run? */
   81 SYSCTL_INT(_kern_smp, OID_AUTO, active, CTLFLAG_RW, &smp_active, 0,
   82     "Number of Auxillary Processors (APs) that were successfully started");
   83 
   84 int smp_disabled = 0;   /* has smp been disabled? */
   85 SYSCTL_INT(_kern_smp, OID_AUTO, disabled, CTLFLAG_RDTUN, &smp_disabled, 0,
   86     "SMP has been disabled from the loader");
   87 TUNABLE_INT("kern.smp.disabled", &smp_disabled);
   88 
   89 int smp_cpus = 1;       /* how many cpu's running */
   90 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD, &smp_cpus, 0,
   91     "Number of CPUs online");
   92 
   93 #ifdef SMP
   94 /* Enable forwarding of a signal to a process running on a different CPU */
   95 static int forward_signal_enabled = 1;
   96 SYSCTL_INT(_kern_smp, OID_AUTO, forward_signal_enabled, CTLFLAG_RW,
   97            &forward_signal_enabled, 0,
   98            "Forwarding of a signal to a process on a different CPU");
   99 
  100 /* Enable forwarding of roundrobin to all other cpus */
  101 static int forward_roundrobin_enabled = 1;
  102 SYSCTL_INT(_kern_smp, OID_AUTO, forward_roundrobin_enabled, CTLFLAG_RW,
  103            &forward_roundrobin_enabled, 0,
  104            "Forwarding of roundrobin to all other CPUs");
  105 
  106 /* Variables needed for SMP rendezvous. */
  107 static void (*smp_rv_setup_func)(void *arg);
  108 static void (*smp_rv_action_func)(void *arg);
  109 static void (*smp_rv_teardown_func)(void *arg);
  110 static void *smp_rv_func_arg;
  111 static volatile int smp_rv_waiters[3];
  112 
  113 /* 
  114  * Shared mutex to restrict busywaits between smp_rendezvous() and
  115  * smp(_targeted)_tlb_shootdown().  A deadlock occurs if both of these
  116  * functions trigger at once and cause multiple CPUs to busywait with
  117  * interrupts disabled. 
  118  */
  119 struct mtx smp_ipi_mtx;
  120 
  121 /*
  122  * Let the MD SMP code initialize mp_maxid very early if it can.
  123  */
  124 static void
  125 mp_setmaxid(void *dummy)
  126 {
  127         cpu_mp_setmaxid();
  128 }
  129 SYSINIT(cpu_mp_setmaxid, SI_SUB_TUNABLES, SI_ORDER_FIRST, mp_setmaxid, NULL)
  130 
  131 /*
  132  * Call the MD SMP initialization code.
  133  */
  134 static void
  135 mp_start(void *dummy)
  136 {
  137 
  138         /* Probe for MP hardware. */
  139         if (smp_disabled != 0 || cpu_mp_probe() == 0) {
  140                 mp_ncpus = 1;
  141                 all_cpus = PCPU_GET(cpumask);
  142                 return;
  143         }
  144 
  145         mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);
  146         cpu_mp_start();
  147         printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
  148             mp_ncpus);
  149         cpu_mp_announce();
  150 }
  151 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL)
  152 
  153 void
  154 forward_signal(struct thread *td)
  155 {
  156         int id;
  157 
  158         /*
  159          * signotify() has already set TDF_ASTPENDING and TDF_NEEDSIGCHECK on
  160          * this thread, so all we need to do is poke it if it is currently
  161          * executing so that it executes ast().
  162          */
  163         THREAD_LOCK_ASSERT(td, MA_OWNED);
  164         KASSERT(TD_IS_RUNNING(td),
  165             ("forward_signal: thread is not TDS_RUNNING"));
  166 
  167         CTR1(KTR_SMP, "forward_signal(%p)", td->td_proc);
  168 
  169         if (!smp_started || cold || panicstr)
  170                 return;
  171         if (!forward_signal_enabled)
  172                 return;
  173 
  174         /* No need to IPI ourself. */
  175         if (td == curthread)
  176                 return;
  177 
  178         id = td->td_oncpu;
  179         if (id == NOCPU)
  180                 return;
  181         ipi_selected(1 << id, IPI_AST);
  182 }
  183 
  184 void
  185 forward_roundrobin(void)
  186 {
  187         struct pcpu *pc;
  188         struct thread *td;
  189         cpumask_t id, map, me;
  190 
  191         CTR0(KTR_SMP, "forward_roundrobin()");
  192 
  193         if (!smp_started || cold || panicstr)
  194                 return;
  195         if (!forward_roundrobin_enabled)
  196                 return;
  197         map = 0;
  198         me = PCPU_GET(cpumask);
  199         SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
  200                 td = pc->pc_curthread;
  201                 id = pc->pc_cpumask;
  202                 if (id != me && (id & stopped_cpus) == 0 &&
  203                     !TD_IS_IDLETHREAD(td)) {
  204                         td->td_flags |= TDF_NEEDRESCHED;
  205                         map |= id;
  206                 }
  207         }
  208         ipi_selected(map, IPI_AST);
  209 }
  210 
  211 /*
  212  * When called the executing CPU will send an IPI to all other CPUs
  213  *  requesting that they halt execution.
  214  *
  215  * Usually (but not necessarily) called with 'other_cpus' as its arg.
  216  *
  217  *  - Signals all CPUs in map to stop.
  218  *  - Waits for each to stop.
  219  *
  220  * Returns:
  221  *  -1: error
  222  *   0: NA
  223  *   1: ok
  224  *
  225  * XXX FIXME: this is not MP-safe, needs a lock to prevent multiple CPUs
  226  *            from executing at same time.
  227  */
  228 int
  229 stop_cpus(cpumask_t map)
  230 {
  231         int i;
  232 
  233         if (!smp_started)
  234                 return 0;
  235 
  236         CTR1(KTR_SMP, "stop_cpus(%x)", map);
  237 
  238         /* send the stop IPI to all CPUs in map */
  239         ipi_selected(map, IPI_STOP);
  240 
  241         i = 0;
  242         while ((stopped_cpus & map) != map) {
  243                 /* spin */
  244                 cpu_spinwait();
  245                 i++;
  246 #ifdef DIAGNOSTIC
  247                 if (i == 100000) {
  248                         printf("timeout stopping cpus\n");
  249                         break;
  250                 }
  251 #endif
  252         }
  253 
  254         return 1;
  255 }
  256 
  257 /*
  258  * Called by a CPU to restart stopped CPUs. 
  259  *
  260  * Usually (but not necessarily) called with 'stopped_cpus' as its arg.
  261  *
  262  *  - Signals all CPUs in map to restart.
  263  *  - Waits for each to restart.
  264  *
  265  * Returns:
  266  *  -1: error
  267  *   0: NA
  268  *   1: ok
  269  */
  270 int
  271 restart_cpus(cpumask_t map)
  272 {
  273 
  274         if (!smp_started)
  275                 return 0;
  276 
  277         CTR1(KTR_SMP, "restart_cpus(%x)", map);
  278 
  279         /* signal other cpus to restart */
  280         atomic_store_rel_int(&started_cpus, map);
  281 
  282         /* wait for each to clear its bit */
  283         while ((stopped_cpus & map) != 0)
  284                 cpu_spinwait();
  285 
  286         return 1;
  287 }
  288 
  289 /*
  290  * All-CPU rendezvous.  CPUs are signalled, all execute the setup function 
  291  * (if specified), rendezvous, execute the action function (if specified),
  292  * rendezvous again, execute the teardown function (if specified), and then
  293  * resume.
  294  *
  295  * Note that the supplied external functions _must_ be reentrant and aware
  296  * that they are running in parallel and in an unknown lock context.
  297  */
  298 void
  299 smp_rendezvous_action(void)
  300 {
  301 
  302         /* Ensure we have up-to-date values. */
  303         atomic_add_acq_int(&smp_rv_waiters[0], 1);
  304         while (smp_rv_waiters[0] < mp_ncpus)
  305                 cpu_spinwait();
  306 
  307         /* setup function */
  308         if (smp_rv_setup_func != NULL)
  309                 smp_rv_setup_func(smp_rv_func_arg);
  310 
  311         /* spin on entry rendezvous */
  312         atomic_add_int(&smp_rv_waiters[1], 1);
  313         while (smp_rv_waiters[1] < mp_ncpus)
  314                 cpu_spinwait();
  315 
  316         /* action function */
  317         if (smp_rv_action_func != NULL)
  318                 smp_rv_action_func(smp_rv_func_arg);
  319 
  320         /* spin on exit rendezvous */
  321         atomic_add_int(&smp_rv_waiters[2], 1);
  322         while (smp_rv_waiters[2] < mp_ncpus)
  323                 cpu_spinwait();
  324 
  325         /* teardown function */
  326         if (smp_rv_teardown_func != NULL)
  327                 smp_rv_teardown_func(smp_rv_func_arg);
  328 }
  329 
  330 void
  331 smp_rendezvous(void (* setup_func)(void *), 
  332                void (* action_func)(void *),
  333                void (* teardown_func)(void *),
  334                void *arg)
  335 {
  336 
  337         if (!smp_started) {
  338                 if (setup_func != NULL)
  339                         setup_func(arg);
  340                 if (action_func != NULL)
  341                         action_func(arg);
  342                 if (teardown_func != NULL)
  343                         teardown_func(arg);
  344                 return;
  345         }
  346                 
  347         /* obtain rendezvous lock */
  348         mtx_lock_spin(&smp_ipi_mtx);
  349 
  350         /* set static function pointers */
  351         smp_rv_setup_func = setup_func;
  352         smp_rv_action_func = action_func;
  353         smp_rv_teardown_func = teardown_func;
  354         smp_rv_func_arg = arg;
  355         smp_rv_waiters[1] = 0;
  356         smp_rv_waiters[2] = 0;
  357         atomic_store_rel_int(&smp_rv_waiters[0], 0);
  358 
  359         /* signal other processors, which will enter the IPI with interrupts off */
  360         ipi_all_but_self(IPI_RENDEZVOUS);
  361 
  362         /* call executor function */
  363         smp_rendezvous_action();
  364 
  365         /* release lock */
  366         mtx_unlock_spin(&smp_ipi_mtx);
  367 }
  368 #else /* !SMP */
  369 
  370 /*
  371  * Provide dummy SMP support for UP kernels.  Modules that need to use SMP
  372  * APIs will still work using this dummy support.
  373  */
  374 static void
  375 mp_setvariables_for_up(void *dummy)
  376 {
  377         mp_ncpus = 1;
  378         mp_maxid = PCPU_GET(cpuid);
  379         all_cpus = PCPU_GET(cpumask);
  380         KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
  381 }
  382 SYSINIT(cpu_mp_setvariables, SI_SUB_TUNABLES, SI_ORDER_FIRST,
  383     mp_setvariables_for_up, NULL)
  384 
  385 void
  386 smp_rendezvous(void (* setup_func)(void *), 
  387                void (* action_func)(void *),
  388                void (* teardown_func)(void *),
  389                void *arg)
  390 {
  391 
  392         if (setup_func != NULL)
  393                 setup_func(arg);
  394         if (action_func != NULL)
  395                 action_func(arg);
  396         if (teardown_func != NULL)
  397                 teardown_func(arg);
  398 }
  399 #endif /* SMP */

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