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: releng/6.1/sys/kern/kern_synch.c 158179 2006-04-30 16:44:43Z cvs2svn $");
   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 thread *td;
  126         struct proc *p;
  127         int catch, rval, flags;
  128         WITNESS_SAVE_DECL(mtx);
  129 
  130         td = curthread;
  131         p = td->td_proc;
  132 #ifdef KTRACE
  133         if (KTRPOINT(td, KTR_CSW))
  134                 ktrcsw(1, 0);
  135 #endif
  136         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, mtx == NULL ? NULL :
  137             &mtx->mtx_object, "Sleeping on \"%s\"", wmesg);
  138         KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL,
  139             ("sleeping without a mutex"));
  140         KASSERT(p != NULL, ("msleep1"));
  141         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  142 
  143         if (cold) {
  144                 /*
  145                  * During autoconfiguration, just return;
  146                  * don't run any other threads or panic below,
  147                  * in case this is the idle thread and already asleep.
  148                  * XXX: this used to do "s = splhigh(); splx(safepri);
  149                  * splx(s);" to give interrupts a chance, but there is
  150                  * no way to give interrupts a chance now.
  151                  */
  152                 if (mtx != NULL && priority & PDROP)
  153                         mtx_unlock(mtx);
  154                 return (0);
  155         }
  156         catch = priority & PCATCH;
  157         rval = 0;
  158 
  159         /*
  160          * If we are already on a sleep queue, then remove us from that
  161          * sleep queue first.  We have to do this to handle recursive
  162          * sleeps.
  163          */
  164         if (TD_ON_SLEEPQ(td))
  165                 sleepq_remove(td, td->td_wchan);
  166 
  167         flags = SLEEPQ_MSLEEP;
  168         if (catch)
  169                 flags |= SLEEPQ_INTERRUPTIBLE;
  170 
  171         sleepq_lock(ident);
  172         CTR5(KTR_PROC, "msleep: thread %p (pid %ld, %s) on %s (%p)",
  173             (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident);
  174 
  175         DROP_GIANT();
  176         if (mtx != NULL) {
  177                 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  178                 WITNESS_SAVE(&mtx->mtx_object, mtx);
  179                 mtx_unlock(mtx);
  180         }
  181 
  182         /*
  183          * We put ourselves on the sleep queue and start our timeout
  184          * before calling thread_suspend_check, as we could stop there,
  185          * and a wakeup or a SIGCONT (or both) could occur while we were
  186          * stopped without resuming us.  Thus, we must be ready for sleep
  187          * when cursig() is called.  If the wakeup happens while we're
  188          * stopped, then td will no longer be on a sleep queue upon
  189          * return from cursig().
  190          */
  191         sleepq_add(ident, mtx, wmesg, flags);
  192         if (timo)
  193                 sleepq_set_timeout(ident, timo);
  194 
  195         /*
  196          * Adjust this thread's priority.
  197          */
  198         mtx_lock_spin(&sched_lock);
  199         sched_prio(td, priority & PRIMASK);
  200         mtx_unlock_spin(&sched_lock);
  201 
  202         if (timo && catch)
  203                 rval = sleepq_timedwait_sig(ident);
  204         else if (timo)
  205                 rval = sleepq_timedwait(ident);
  206         else if (catch)
  207                 rval = sleepq_wait_sig(ident);
  208         else {
  209                 sleepq_wait(ident);
  210                 rval = 0;
  211         }
  212 #ifdef KTRACE
  213         if (KTRPOINT(td, KTR_CSW))
  214                 ktrcsw(0, 0);
  215 #endif
  216         PICKUP_GIANT();
  217         if (mtx != NULL && !(priority & PDROP)) {
  218                 mtx_lock(mtx);
  219                 WITNESS_RESTORE(&mtx->mtx_object, mtx);
  220         }
  221         return (rval);
  222 }
  223 
  224 /*
  225  * Make all threads sleeping on the specified identifier runnable.
  226  */
  227 void
  228 wakeup(ident)
  229         register void *ident;
  230 {
  231 
  232         sleepq_lock(ident);
  233         sleepq_broadcast(ident, SLEEPQ_MSLEEP, -1);
  234 }
  235 
  236 /*
  237  * Make a thread sleeping on the specified identifier runnable.
  238  * May wake more than one thread if a target thread is currently
  239  * swapped out.
  240  */
  241 void
  242 wakeup_one(ident)
  243         register void *ident;
  244 {
  245 
  246         sleepq_lock(ident);
  247         sleepq_signal(ident, SLEEPQ_MSLEEP, -1);
  248 }
  249 
  250 /*
  251  * The machine independent parts of context switching.
  252  */
  253 void
  254 mi_switch(int flags, struct thread *newtd)
  255 {
  256         struct bintime new_switchtime;
  257         struct thread *td;
  258         struct proc *p;
  259 
  260         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  261         td = curthread;                 /* XXX */
  262         p = td->td_proc;                /* XXX */
  263         KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
  264 #ifdef INVARIANTS
  265         if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
  266                 mtx_assert(&Giant, MA_NOTOWNED);
  267 #endif
  268         KASSERT(td->td_critnest == 1 || (td->td_critnest == 2 &&
  269             (td->td_owepreempt) && (flags & SW_INVOL) != 0 &&
  270             newtd == NULL) || panicstr,
  271             ("mi_switch: switch in a critical section"));
  272         KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
  273             ("mi_switch: switch must be voluntary or involuntary"));
  274         KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
  275 
  276         if (flags & SW_VOL)
  277                 p->p_stats->p_ru.ru_nvcsw++;
  278         else
  279                 p->p_stats->p_ru.ru_nivcsw++;
  280 
  281         /*
  282          * Compute the amount of time during which the current
  283          * process was running, and add that to its total so far.
  284          */
  285         binuptime(&new_switchtime);
  286         bintime_add(&p->p_rux.rux_runtime, &new_switchtime);
  287         bintime_sub(&p->p_rux.rux_runtime, PCPU_PTR(switchtime));
  288 
  289         td->td_generation++;    /* bump preempt-detect counter */
  290 
  291         /*
  292          * Don't perform context switches from the debugger.
  293          */
  294         if (kdb_active) {
  295                 mtx_unlock_spin(&sched_lock);
  296                 kdb_backtrace();
  297                 kdb_reenter();
  298                 panic("%s: did not reenter debugger", __func__);
  299         }
  300 
  301         /*
  302          * Check if the process exceeds its cpu resource allocation.  If
  303          * it reaches the max, arrange to kill the process in ast().
  304          */
  305         if (p->p_cpulimit != RLIM_INFINITY &&
  306             p->p_rux.rux_runtime.sec >= p->p_cpulimit) {
  307                 p->p_sflag |= PS_XCPU;
  308                 td->td_flags |= TDF_ASTPENDING;
  309         }
  310 
  311         /*
  312          * Finish up stats for outgoing thread.
  313          */
  314         cnt.v_swtch++;
  315         PCPU_SET(switchtime, new_switchtime);
  316         PCPU_SET(switchticks, ticks);
  317         CTR4(KTR_PROC, "mi_switch: old thread %p (kse %p, pid %ld, %s)",
  318             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  319         if ((flags & SW_VOL) && (td->td_proc->p_flag & P_SA))
  320                 newtd = thread_switchout(td, flags, newtd);
  321 #if (KTR_COMPILE & KTR_SCHED) != 0
  322         if (td == PCPU_GET(idlethread))
  323                 CTR3(KTR_SCHED, "mi_switch: %p(%s) prio %d idle",
  324                     td, td->td_proc->p_comm, td->td_priority);
  325         else if (newtd != NULL)
  326                 CTR5(KTR_SCHED,
  327                     "mi_switch: %p(%s) prio %d preempted by %p(%s)",
  328                     td, td->td_proc->p_comm, td->td_priority, newtd,
  329                     newtd->td_proc->p_comm);
  330         else
  331                 CTR6(KTR_SCHED,
  332                     "mi_switch: %p(%s) prio %d inhibit %d wmesg %s lock %s",
  333                     td, td->td_proc->p_comm, td->td_priority,
  334                     td->td_inhibitors, td->td_wmesg, td->td_lockname);
  335 #endif
  336         sched_switch(td, newtd, flags);
  337         CTR3(KTR_SCHED, "mi_switch: running %p(%s) prio %d",
  338             td, td->td_proc->p_comm, td->td_priority);
  339 
  340         CTR4(KTR_PROC, "mi_switch: new thread %p (kse %p, pid %ld, %s)",
  341             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  342 
  343         /* 
  344          * If the last thread was exiting, finish cleaning it up.
  345          */
  346         if ((td = PCPU_GET(deadthread))) {
  347                 PCPU_SET(deadthread, NULL);
  348                 thread_stash(td);
  349         }
  350 }
  351 
  352 /*
  353  * Change process state to be runnable,
  354  * placing it on the run queue if it is in memory,
  355  * and awakening the swapper if it isn't in memory.
  356  */
  357 void
  358 setrunnable(struct thread *td)
  359 {
  360         struct proc *p;
  361 
  362         p = td->td_proc;
  363         mtx_assert(&sched_lock, MA_OWNED);
  364         switch (p->p_state) {
  365         case PRS_ZOMBIE:
  366                 panic("setrunnable(1)");
  367         default:
  368                 break;
  369         }
  370         switch (td->td_state) {
  371         case TDS_RUNNING:
  372         case TDS_RUNQ:
  373                 return;
  374         case TDS_INHIBITED:
  375                 /*
  376                  * If we are only inhibited because we are swapped out
  377                  * then arange to swap in this process. Otherwise just return.
  378                  */
  379                 if (td->td_inhibitors != TDI_SWAPPED)
  380                         return;
  381                 /* XXX: intentional fall-through ? */
  382         case TDS_CAN_RUN:
  383                 break;
  384         default:
  385                 printf("state is 0x%x", td->td_state);
  386                 panic("setrunnable(2)");
  387         }
  388         if ((p->p_sflag & PS_INMEM) == 0) {
  389                 if ((p->p_sflag & PS_SWAPPINGIN) == 0) {
  390                         p->p_sflag |= PS_SWAPINREQ;
  391                         /*
  392                          * due to a LOR between sched_lock and
  393                          * the sleepqueue chain locks, use
  394                          * lower level scheduling functions.
  395                          */
  396                         kick_proc0();
  397                 }
  398         } else
  399                 sched_wakeup(td);
  400 }
  401 
  402 /*
  403  * Compute a tenex style load average of a quantity on
  404  * 1, 5 and 15 minute intervals.
  405  * XXXKSE   Needs complete rewrite when correct info is available.
  406  * Completely Bogus.. only works with 1:1 (but compiles ok now :-)
  407  */
  408 static void
  409 loadav(void *arg)
  410 {
  411         int i, nrun;
  412         struct loadavg *avg;
  413 
  414         nrun = sched_load();
  415         avg = &averunnable;
  416 
  417         for (i = 0; i < 3; i++)
  418                 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
  419                     nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
  420 
  421         /*
  422          * Schedule the next update to occur after 5 seconds, but add a
  423          * random variation to avoid synchronisation with processes that
  424          * run at regular intervals.
  425          */
  426         callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
  427             loadav, NULL);
  428 }
  429 
  430 static void
  431 lboltcb(void *arg)
  432 {
  433         wakeup(&lbolt);
  434         callout_reset(&lbolt_callout, hz, lboltcb, NULL);
  435 }
  436 
  437 /* ARGSUSED */
  438 static void
  439 synch_setup(dummy)
  440         void *dummy;
  441 {
  442         callout_init(&loadav_callout, CALLOUT_MPSAFE);
  443         callout_init(&lbolt_callout, CALLOUT_MPSAFE);
  444 
  445         /* Kick off timeout driven events by calling first time. */
  446         loadav(NULL);
  447         lboltcb(NULL);
  448 }
  449 
  450 /*
  451  * General purpose yield system call
  452  */
  453 int
  454 yield(struct thread *td, struct yield_args *uap)
  455 {
  456         struct ksegrp *kg;
  457 
  458         kg = td->td_ksegrp;
  459         mtx_assert(&Giant, MA_NOTOWNED);
  460         mtx_lock_spin(&sched_lock);
  461         sched_prio(td, PRI_MAX_TIMESHARE);
  462         mi_switch(SW_VOL, NULL);
  463         mtx_unlock_spin(&sched_lock);
  464         td->td_retval[0] = 0;
  465         return (0);
  466 }

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