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/kern_synch.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1990, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_synch.c        8.9 (Berkeley) 5/19/95
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: src/sys/kern/kern_synch.c,v 1.257.2.9 2005/12/05 20:14:56 jhb Exp $");
   39 
   40 #include "opt_ktrace.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/condvar.h>
   45 #include <sys/kdb.h>
   46 #include <sys/kernel.h>
   47 #include <sys/ktr.h>
   48 #include <sys/lock.h>
   49 #include <sys/mutex.h>
   50 #include <sys/proc.h>
   51 #include <sys/resourcevar.h>
   52 #include <sys/sched.h>
   53 #include <sys/signalvar.h>
   54 #include <sys/sleepqueue.h>
   55 #include <sys/smp.h>
   56 #include <sys/sx.h>
   57 #include <sys/sysctl.h>
   58 #include <sys/sysproto.h>
   59 #include <sys/vmmeter.h>
   60 #ifdef KTRACE
   61 #include <sys/uio.h>
   62 #include <sys/ktrace.h>
   63 #endif
   64 
   65 #include <machine/cpu.h>
   66 
   67 static void synch_setup(void *dummy);
   68 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, NULL)
   69 
   70 int     hogticks;
   71 int     lbolt;
   72 
   73 static struct callout loadav_callout;
   74 static struct callout lbolt_callout;
   75 
   76 struct loadavg averunnable =
   77         { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
   78 /*
   79  * Constants for averages over 1, 5, and 15 minutes
   80  * when sampling at 5 second intervals.
   81  */
   82 static fixpt_t cexp[3] = {
   83         0.9200444146293232 * FSCALE,    /* exp(-1/12) */
   84         0.9834714538216174 * FSCALE,    /* exp(-1/60) */
   85         0.9944598480048967 * FSCALE,    /* exp(-1/180) */
   86 };
   87 
   88 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
   89 static int      fscale __unused = FSCALE;
   90 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
   91 
   92 static void     loadav(void *arg);
   93 static void     lboltcb(void *arg);
   94 
   95 void
   96 sleepinit(void)
   97 {
   98 
   99         hogticks = (hz / 10) * 2;       /* Default only. */
  100         init_sleepqueues();
  101 }
  102 
  103 /*
  104  * General sleep call.  Suspends the current process until a wakeup is
  105  * performed on the specified identifier.  The process will then be made
  106  * runnable with the specified priority.  Sleeps at most timo/hz seconds
  107  * (0 means no timeout).  If pri includes PCATCH flag, signals are checked
  108  * before and after sleeping, else signals are not checked.  Returns 0 if
  109  * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
  110  * signal needs to be delivered, ERESTART is returned if the current system
  111  * call should be restarted if possible, and EINTR is returned if the system
  112  * call should be interrupted by the signal (return EINTR).
  113  *
  114  * The mutex argument is exited before the caller is suspended, and
  115  * entered before msleep returns.  If priority includes the PDROP
  116  * flag the mutex is not entered before returning.
  117  */
  118 int
  119 msleep(ident, mtx, priority, wmesg, timo)
  120         void *ident;
  121         struct mtx *mtx;
  122         int priority, timo;
  123         const char *wmesg;
  124 {
  125         struct sleepqueue *sq;
  126         struct thread *td;
  127         struct proc *p;
  128         int catch, rval, sig, flags;
  129         WITNESS_SAVE_DECL(mtx);
  130 
  131         td = curthread;
  132         p = td->td_proc;
  133 #ifdef KTRACE
  134         if (KTRPOINT(td, KTR_CSW))
  135                 ktrcsw(1, 0);
  136 #endif
  137         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, mtx == NULL ? NULL :
  138             &mtx->mtx_object, "Sleeping on \"%s\"", wmesg);
  139         KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL,
  140             ("sleeping without a mutex"));
  141         KASSERT(p != NULL, ("msleep1"));
  142         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  143 
  144         if (cold) {
  145                 /*
  146                  * During autoconfiguration, just return;
  147                  * don't run any other threads or panic below,
  148                  * in case this is the idle thread and already asleep.
  149                  * XXX: this used to do "s = splhigh(); splx(safepri);
  150                  * splx(s);" to give interrupts a chance, but there is
  151                  * no way to give interrupts a chance now.
  152                  */
  153                 if (mtx != NULL && priority & PDROP)
  154                         mtx_unlock(mtx);
  155                 return (0);
  156         }
  157         catch = priority & PCATCH;
  158         rval = 0;
  159 
  160         /*
  161          * If we are already on a sleep queue, then remove us from that
  162          * sleep queue first.  We have to do this to handle recursive
  163          * sleeps.
  164          */
  165         if (TD_ON_SLEEPQ(td))
  166                 sleepq_remove(td, td->td_wchan);
  167 
  168         sq = sleepq_lookup(ident);
  169         if (catch) {
  170                 /*
  171                  * Don't bother sleeping if we are exiting and not the exiting
  172                  * thread or if our thread is marked as interrupted.
  173                  */
  174                 mtx_lock_spin(&sched_lock);
  175                 rval = thread_sleep_check(td);
  176                 mtx_unlock_spin(&sched_lock);
  177                 if (rval != 0) {
  178                         sleepq_release(ident);
  179                         return (rval);
  180                 }
  181         }
  182         CTR5(KTR_PROC, "msleep: thread %p (pid %ld, %s) on %s (%p)",
  183             (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident);
  184 
  185         DROP_GIANT();
  186         if (mtx != NULL) {
  187                 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  188                 WITNESS_SAVE(&mtx->mtx_object, mtx);
  189                 mtx_unlock(mtx);
  190         }
  191 
  192         /*
  193          * We put ourselves on the sleep queue and start our timeout
  194          * before calling thread_suspend_check, as we could stop there,
  195          * and a wakeup or a SIGCONT (or both) could occur while we were
  196          * stopped without resuming us.  Thus, we must be ready for sleep
  197          * when cursig() is called.  If the wakeup happens while we're
  198          * stopped, then td will no longer be on a sleep queue upon
  199          * return from cursig().
  200          */
  201         flags = SLEEPQ_MSLEEP;
  202         if (catch)
  203                 flags |= SLEEPQ_INTERRUPTIBLE;
  204         sleepq_add(sq, ident, mtx, wmesg, flags);
  205         if (timo)
  206                 sleepq_set_timeout(ident, timo);
  207         if (catch) {
  208                 sig = sleepq_catch_signals(ident);
  209         } else
  210                 sig = 0;
  211 
  212         /*
  213          * Adjust this thread's priority.
  214          *
  215          * XXX: do we need to save priority in td_base_pri?
  216          */
  217         mtx_lock_spin(&sched_lock);
  218         sched_prio(td, priority & PRIMASK);
  219         mtx_unlock_spin(&sched_lock);
  220 
  221         if (timo && catch)
  222                 rval = sleepq_timedwait_sig(ident, sig != 0);
  223         else if (timo)
  224                 rval = sleepq_timedwait(ident);
  225         else if (catch)
  226                 rval = sleepq_wait_sig(ident);
  227         else {
  228                 sleepq_wait(ident);
  229                 rval = 0;
  230         }
  231         if (rval == 0 && catch)
  232                 rval = sleepq_calc_signal_retval(sig);
  233 #ifdef KTRACE
  234         if (KTRPOINT(td, KTR_CSW))
  235                 ktrcsw(0, 0);
  236 #endif
  237         PICKUP_GIANT();
  238         if (mtx != NULL && !(priority & PDROP)) {
  239                 mtx_lock(mtx);
  240                 WITNESS_RESTORE(&mtx->mtx_object, mtx);
  241         }
  242         return (rval);
  243 }
  244 
  245 /*
  246  * Make all threads sleeping on the specified identifier runnable.
  247  */
  248 void
  249 wakeup(ident)
  250         register void *ident;
  251 {
  252 
  253         sleepq_broadcast(ident, SLEEPQ_MSLEEP, -1);
  254 }
  255 
  256 /*
  257  * Make a thread sleeping on the specified identifier runnable.
  258  * May wake more than one thread if a target thread is currently
  259  * swapped out.
  260  */
  261 void
  262 wakeup_one(ident)
  263         register void *ident;
  264 {
  265 
  266         sleepq_signal(ident, SLEEPQ_MSLEEP, -1);
  267 }
  268 
  269 /*
  270  * The machine independent parts of context switching.
  271  */
  272 void
  273 mi_switch(int flags, struct thread *newtd)
  274 {
  275         struct bintime new_switchtime;
  276         struct thread *td;
  277         struct proc *p;
  278 
  279         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  280         td = curthread;                 /* XXX */
  281         p = td->td_proc;                /* XXX */
  282         KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
  283 #ifdef INVARIANTS
  284         if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
  285                 mtx_assert(&Giant, MA_NOTOWNED);
  286 #endif
  287         KASSERT(td->td_critnest == 1 || (td->td_critnest == 2 &&
  288             (td->td_pflags & TDP_OWEPREEMPT) != 0 && (flags & SW_INVOL) != 0 &&
  289             newtd == NULL),
  290             ("mi_switch: switch in a critical section"));
  291         KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
  292             ("mi_switch: switch must be voluntary or involuntary"));
  293         KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
  294 
  295         if (flags & SW_VOL)
  296                 p->p_stats->p_ru.ru_nvcsw++;
  297         else
  298                 p->p_stats->p_ru.ru_nivcsw++;
  299 
  300         /*
  301          * Compute the amount of time during which the current
  302          * process was running, and add that to its total so far.
  303          */
  304         binuptime(&new_switchtime);
  305         bintime_add(&p->p_runtime, &new_switchtime);
  306         bintime_sub(&p->p_runtime, PCPU_PTR(switchtime));
  307 
  308         td->td_generation++;    /* bump preempt-detect counter */
  309 
  310         /*
  311          * Don't perform context switches from the debugger.
  312          */
  313         if (kdb_active) {
  314                 mtx_unlock_spin(&sched_lock);
  315                 kdb_backtrace();
  316                 kdb_reenter();
  317                 panic("%s: did not reenter debugger", __func__);
  318         }
  319 
  320         /*
  321          * Check if the process exceeds its cpu resource allocation.  If
  322          * it reaches the max, arrange to kill the process in ast().
  323          */
  324         if (p->p_cpulimit != RLIM_INFINITY &&
  325             p->p_runtime.sec >= p->p_cpulimit) {
  326                 p->p_sflag |= PS_XCPU;
  327                 td->td_flags |= TDF_ASTPENDING;
  328         }
  329 
  330         /*
  331          * Finish up stats for outgoing thread.
  332          */
  333         cnt.v_swtch++;
  334         PCPU_SET(switchtime, new_switchtime);
  335         PCPU_SET(switchticks, ticks);
  336         CTR4(KTR_PROC, "mi_switch: old thread %p (kse %p, pid %ld, %s)",
  337             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  338         if ((flags & SW_VOL) && (td->td_proc->p_flag & P_SA))
  339                 newtd = thread_switchout(td, flags, newtd);
  340 #if (KTR_COMPILE & KTR_SCHED) != 0
  341         if (td == PCPU_GET(idlethread))
  342                 CTR3(KTR_SCHED, "mi_switch: %p(%s) prio %d idle",
  343                     td, td->td_proc->p_comm, td->td_priority);
  344         else if (newtd != NULL)
  345                 CTR5(KTR_SCHED,
  346                     "mi_switch: %p(%s) prio %d preempted by %p(%s)",
  347                     td, td->td_proc->p_comm, td->td_priority, newtd,
  348                     newtd->td_proc->p_comm);
  349         else
  350                 CTR6(KTR_SCHED,
  351                     "mi_switch: %p(%s) prio %d inhibit %d wmesg %s lock %s",
  352                     td, td->td_proc->p_comm, td->td_priority,
  353                     td->td_inhibitors, td->td_wmesg, td->td_lockname);
  354 #endif
  355         sched_switch(td, newtd, flags);
  356         CTR3(KTR_SCHED, "mi_switch: running %p(%s) prio %d",
  357             td, td->td_proc->p_comm, td->td_priority);
  358 
  359         CTR4(KTR_PROC, "mi_switch: new thread %p (kse %p, pid %ld, %s)",
  360             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  361 
  362         /* 
  363          * If the last thread was exiting, finish cleaning it up.
  364          */
  365         if ((td = PCPU_GET(deadthread))) {
  366                 PCPU_SET(deadthread, NULL);
  367                 thread_stash(td);
  368         }
  369 }
  370 
  371 /*
  372  * Change process state to be runnable,
  373  * placing it on the run queue if it is in memory,
  374  * and awakening the swapper if it isn't in memory.
  375  */
  376 void
  377 setrunnable(struct thread *td)
  378 {
  379         struct proc *p;
  380 
  381         p = td->td_proc;
  382         mtx_assert(&sched_lock, MA_OWNED);
  383         switch (p->p_state) {
  384         case PRS_ZOMBIE:
  385                 panic("setrunnable(1)");
  386         default:
  387                 break;
  388         }
  389         switch (td->td_state) {
  390         case TDS_RUNNING:
  391         case TDS_RUNQ:
  392                 return;
  393         case TDS_INHIBITED:
  394                 /*
  395                  * If we are only inhibited because we are swapped out
  396                  * then arange to swap in this process. Otherwise just return.
  397                  */
  398                 if (td->td_inhibitors != TDI_SWAPPED)
  399                         return;
  400                 /* XXX: intentional fall-through ? */
  401         case TDS_CAN_RUN:
  402                 break;
  403         default:
  404                 printf("state is 0x%x", td->td_state);
  405                 panic("setrunnable(2)");
  406         }
  407         if ((p->p_sflag & PS_INMEM) == 0) {
  408                 if ((p->p_sflag & PS_SWAPPINGIN) == 0) {
  409                         p->p_sflag |= PS_SWAPINREQ;
  410                         /*
  411                          * due to a LOR between sched_lock and
  412                          * the sleepqueue chain locks, delay
  413                          * wakeup proc0 until thread leaves
  414                          * critical region.
  415                          */
  416                         curthread->td_pflags |= TDP_WAKEPROC0;
  417                 }
  418         } else
  419                 sched_wakeup(td);
  420 }
  421 
  422 /*
  423  * Compute a tenex style load average of a quantity on
  424  * 1, 5 and 15 minute intervals.
  425  * XXXKSE   Needs complete rewrite when correct info is available.
  426  * Completely Bogus.. only works with 1:1 (but compiles ok now :-)
  427  */
  428 static void
  429 loadav(void *arg)
  430 {
  431         int i, nrun;
  432         struct loadavg *avg;
  433 
  434         nrun = sched_load();
  435         avg = &averunnable;
  436 
  437         for (i = 0; i < 3; i++)
  438                 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
  439                     nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
  440 
  441         /*
  442          * Schedule the next update to occur after 5 seconds, but add a
  443          * random variation to avoid synchronisation with processes that
  444          * run at regular intervals.
  445          */
  446         callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
  447             loadav, NULL);
  448 }
  449 
  450 static void
  451 lboltcb(void *arg)
  452 {
  453         wakeup(&lbolt);
  454         callout_reset(&lbolt_callout, hz, lboltcb, NULL);
  455 }
  456 
  457 /* ARGSUSED */
  458 static void
  459 synch_setup(dummy)
  460         void *dummy;
  461 {
  462         callout_init(&loadav_callout, CALLOUT_MPSAFE);
  463         callout_init(&lbolt_callout, CALLOUT_MPSAFE);
  464 
  465         /* Kick off timeout driven events by calling first time. */
  466         loadav(NULL);
  467         lboltcb(NULL);
  468 }
  469 
  470 /*
  471  * General purpose yield system call
  472  */
  473 int
  474 yield(struct thread *td, struct yield_args *uap)
  475 {
  476         struct ksegrp *kg;
  477 
  478         kg = td->td_ksegrp;
  479         mtx_assert(&Giant, MA_NOTOWNED);
  480         mtx_lock_spin(&sched_lock);
  481         sched_prio(td, PRI_MAX_TIMESHARE);
  482         mi_switch(SW_VOL, NULL);
  483         mtx_unlock_spin(&sched_lock);
  484         td->td_retval[0] = 0;
  485         return (0);
  486 }

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