FreeBSD/Linux Kernel Cross Reference
sys/kern/sched_4bsd.c

     /*-
      * Copyright (c) 1982, 1986, 1990, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
      * the permission of UNIX System Laboratories, Inc.
      *
     * 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. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
     *
     * $FreeBSD: releng/5.0/sys/kern/sched_4bsd.c 107137 2002-11-21 09:30:55Z jeff $
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/ktr.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/sx.h>
    
    /*
     * INVERSE_ESTCPU_WEIGHT is only suitable for statclock() frequencies in
     * the range 100-256 Hz (approximately).
     */
    #define ESTCPULIM(e) \
        min((e), INVERSE_ESTCPU_WEIGHT * (NICE_WEIGHT * (PRIO_MAX - PRIO_MIN) - \
        RQ_PPQ) + INVERSE_ESTCPU_WEIGHT - 1)
    #define INVERSE_ESTCPU_WEIGHT   8       /* 1 / (priorities per estcpu level). */
    #define NICE_WEIGHT             1       /* Priorities per nice level. */
    
    struct ke_sched *kse0_sched = NULL;
    struct kg_sched *ksegrp0_sched = NULL;
    struct p_sched *proc0_sched = NULL;
    struct td_sched *thread0_sched = NULL;
    
    static int      sched_quantum;  /* Roundrobin scheduling quantum in ticks. */
    #define SCHED_QUANTUM   (hz / 10);      /* Default sched quantum */
    
    static struct callout schedcpu_callout;
    static struct callout roundrobin_callout;
    
    static void     roundrobin(void *arg);
    static void     schedcpu(void *arg);
    static void     sched_setup(void *dummy);
    static void     maybe_resched(struct thread *td);
    static void     updatepri(struct ksegrp *kg);
    static void     resetpriority(struct ksegrp *kg);
    
    SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)
    
    /*
     * Global run queue.
     */
    static struct runq runq;
    SYSINIT(runq, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, runq_init, &runq)
    
    static int
    sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
    {
            int error, new_val;
    
            new_val = sched_quantum * tick;
            error = sysctl_handle_int(oidp, &new_val, 0, req);
            if (error != 0 || req->newptr == NULL)
                    return (error);
            if (new_val < tick)
                   return (EINVAL);
           sched_quantum = new_val / tick;
           hogticks = 2 * sched_quantum;
           return (0);
   }
   
   SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
           0, sizeof sched_quantum, sysctl_kern_quantum, "I",
           "Roundrobin scheduling quantum in microseconds");
   
   /*
    * Arrange to reschedule if necessary, taking the priorities and
    * schedulers into account.
    */
   static void
   maybe_resched(struct thread *td)
   {
   
           mtx_assert(&sched_lock, MA_OWNED);
           if (td->td_priority < curthread->td_priority)
                   curthread->td_kse->ke_flags |= KEF_NEEDRESCHED;
   }
   
   /*
    * Force switch among equal priority processes every 100ms.
    * We don't actually need to force a context switch of the current process.
    * The act of firing the event triggers a context switch to softclock() and
    * then switching back out again which is equivalent to a preemption, thus
    * no further work is needed on the local CPU.
    */
   /* ARGSUSED */
   static void
   roundrobin(void *arg)
   {
   
   #ifdef SMP
           mtx_lock_spin(&sched_lock);
           forward_roundrobin();
           mtx_unlock_spin(&sched_lock);
   #endif
   
           callout_reset(&roundrobin_callout, sched_quantum, roundrobin, NULL);
   }
   
   /*
    * Constants for digital decay and forget:
    *      90% of (p_estcpu) usage in 5 * loadav time
    *      95% of (p_pctcpu) usage in 60 seconds (load insensitive)
    *          Note that, as ps(1) mentions, this can let percentages
    *          total over 100% (I've seen 137.9% for 3 processes).
    *
    * Note that schedclock() updates p_estcpu and p_cpticks asynchronously.
    *
    * We wish to decay away 90% of p_estcpu in (5 * loadavg) seconds.
    * That is, the system wants to compute a value of decay such
    * that the following for loop:
    *      for (i = 0; i < (5 * loadavg); i++)
    *              p_estcpu *= decay;
    * will compute
    *      p_estcpu *= 0.1;
    * for all values of loadavg:
    *
    * Mathematically this loop can be expressed by saying:
    *      decay ** (5 * loadavg) ~= .1
    *
    * The system computes decay as:
    *      decay = (2 * loadavg) / (2 * loadavg + 1)
    *
    * We wish to prove that the system's computation of decay
    * will always fulfill the equation:
    *      decay ** (5 * loadavg) ~= .1
    *
    * If we compute b as:
    *      b = 2 * loadavg
    * then
    *      decay = b / (b + 1)
    *
    * We now need to prove two things:
    *      1) Given factor ** (5 * loadavg) ~= .1, prove factor == b/(b+1)
    *      2) Given b/(b+1) ** power ~= .1, prove power == (5 * loadavg)
    *
    * Facts:
    *         For x close to zero, exp(x) =~ 1 + x, since
    *              exp(x) = 0! + x**1/1! + x**2/2! + ... .
    *              therefore exp(-1/b) =~ 1 - (1/b) = (b-1)/b.
    *         For x close to zero, ln(1+x) =~ x, since
    *              ln(1+x) = x - x**2/2 + x**3/3 - ...     -1 < x < 1
    *              therefore ln(b/(b+1)) = ln(1 - 1/(b+1)) =~ -1/(b+1).
    *         ln(.1) =~ -2.30
    *
    * Proof of (1):
    *    Solve (factor)**(power) =~ .1 given power (5*loadav):
    *      solving for factor,
    *      ln(factor) =~ (-2.30/5*loadav), or
    *      factor =~ exp(-1/((5/2.30)*loadav)) =~ exp(-1/(2*loadav)) =
    *          exp(-1/b) =~ (b-1)/b =~ b/(b+1).                    QED
    *
    * Proof of (2):
    *    Solve (factor)**(power) =~ .1 given factor == (b/(b+1)):
    *      solving for power,
    *      power*ln(b/(b+1)) =~ -2.30, or
    *      power =~ 2.3 * (b + 1) = 4.6*loadav + 2.3 =~ 5*loadav.  QED
    *
    * Actual power values for the implemented algorithm are as follows:
    *      loadav: 1       2       3       4
    *      power:  5.68    10.32   14.94   19.55
    */
   
   /* calculations for digital decay to forget 90% of usage in 5*loadav sec */
   #define loadfactor(loadav)      (2 * (loadav))
   #define decay_cpu(loadfac, cpu) (((loadfac) * (cpu)) / ((loadfac) + FSCALE))
   
   /* decay 95% of `p_pctcpu' in 60 seconds; see CCPU_SHIFT before changing */
   static fixpt_t  ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */
   SYSCTL_INT(_kern, OID_AUTO, ccpu, CTLFLAG_RD, &ccpu, 0, "");
   
   /*
    * If `ccpu' is not equal to `exp(-1/20)' and you still want to use the
    * faster/more-accurate formula, you'll have to estimate CCPU_SHIFT below
    * and possibly adjust FSHIFT in "param.h" so that (FSHIFT >= CCPU_SHIFT).
    *
    * To estimate CCPU_SHIFT for exp(-1/20), the following formula was used:
    *      1 - exp(-1/20) ~= 0.0487 ~= 0.0488 == 1 (fixed pt, *11* bits).
    *
    * If you don't want to bother with the faster/more-accurate formula, you
    * can set CCPU_SHIFT to (FSHIFT + 1) which will use a slower/less-accurate
    * (more general) method of calculating the %age of CPU used by a process.
    */
   #define CCPU_SHIFT      11
   
   /*
    * Recompute process priorities, every hz ticks.
    * MP-safe, called without the Giant mutex.
    */
   /* ARGSUSED */
   static void
   schedcpu(void *arg)
   {
           register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
           struct thread *td;
           struct proc *p;
           struct kse *ke;
           struct ksegrp *kg;
           int realstathz;
           int awake;
   
           realstathz = stathz ? stathz : hz;
           sx_slock(&allproc_lock);
           FOREACH_PROC_IN_SYSTEM(p) {
                   mtx_lock_spin(&sched_lock);
                   p->p_swtime++;
                   FOREACH_KSEGRP_IN_PROC(p, kg) { 
                           awake = 0;
                           FOREACH_KSE_IN_GROUP(kg, ke) {
                                   /*
                                    * Increment time in/out of memory and sleep
                                    * time (if sleeping).  We ignore overflow;
                                    * with 16-bit int's (remember them?)
                                    * overflow takes 45 days.
                                    */
                                   /*
                                    * The kse slptimes are not touched in wakeup
                                    * because the thread may not HAVE a KSE.
                                    */
                                   if (ke->ke_state == KES_ONRUNQ) {
                                           awake = 1;
                                           ke->ke_flags &= ~KEF_DIDRUN;
                                   } else if ((ke->ke_state == KES_THREAD) &&
                                       (TD_IS_RUNNING(ke->ke_thread))) {
                                           awake = 1;
                                           /* Do not clear KEF_DIDRUN */
                                   } else if (ke->ke_flags & KEF_DIDRUN) {
                                           awake = 1;
                                           ke->ke_flags &= ~KEF_DIDRUN;
                                   }
   
                                   /*
                                    * pctcpu is only for ps?
                                    * Do it per kse.. and add them up at the end?
                                    * XXXKSE
                                    */
                                   ke->ke_pctcpu
                                       = (ke->ke_pctcpu * ccpu) >> FSHIFT;
                                   /*
                                    * If the kse has been idle the entire second,
                                    * stop recalculating its priority until
                                    * it wakes up.
                                    */
                                   if (ke->ke_cpticks == 0)
                                           continue;
   #if     (FSHIFT >= CCPU_SHIFT)
                                   ke->ke_pctcpu += (realstathz == 100) ?
                                       ((fixpt_t) ke->ke_cpticks) <<
                                       (FSHIFT - CCPU_SHIFT) :
                                       100 * (((fixpt_t) ke->ke_cpticks) <<
                                       (FSHIFT - CCPU_SHIFT)) / realstathz;
   #else
                                   ke->ke_pctcpu += ((FSCALE - ccpu) *
                                       (ke->ke_cpticks * FSCALE / realstathz)) >>
                                       FSHIFT;
   #endif
                                   ke->ke_cpticks = 0;
                           } /* end of kse loop */
                           /* 
                            * If there are ANY running threads in this KSEGRP,
                            * then don't count it as sleeping.
                            */
                           if (awake) {
                                   if (kg->kg_slptime > 1) {
                                           /*
                                            * In an ideal world, this should not
                                            * happen, because whoever woke us
                                            * up from the long sleep should have
                                            * unwound the slptime and reset our
                                            * priority before we run at the stale
                                            * priority.  Should KASSERT at some
                                            * point when all the cases are fixed.
                                            */
                                           updatepri(kg);
                                   }
                                   kg->kg_slptime = 0;
                           } else {
                                   kg->kg_slptime++;
                           }
                           if (kg->kg_slptime > 1)
                                   continue;
                           kg->kg_estcpu = decay_cpu(loadfac, kg->kg_estcpu);
                           resetpriority(kg);
                           FOREACH_THREAD_IN_GROUP(kg, td) {
                                   if (td->td_priority >= PUSER) {
                                           sched_prio(td, kg->kg_user_pri);
                                   }
                           }
                   } /* end of ksegrp loop */
                   mtx_unlock_spin(&sched_lock);
           } /* end of process loop */
           sx_sunlock(&allproc_lock);
           callout_reset(&schedcpu_callout, hz, schedcpu, NULL);
   }
   
   /*
    * Recalculate the priority of a process after it has slept for a while.
    * For all load averages >= 1 and max p_estcpu of 255, sleeping for at
    * least six times the loadfactor will decay p_estcpu to zero.
    */
   static void
   updatepri(struct ksegrp *kg)
   {
           register unsigned int newcpu;
           register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]);
   
           newcpu = kg->kg_estcpu;
           if (kg->kg_slptime > 5 * loadfac)
                   kg->kg_estcpu = 0;
           else {
                   kg->kg_slptime--;       /* the first time was done in schedcpu */
                   while (newcpu && --kg->kg_slptime)
                           newcpu = decay_cpu(loadfac, newcpu);
                   kg->kg_estcpu = newcpu;
           }
           resetpriority(kg);
   }
   
   /*
    * Compute the priority of a process when running in user mode.
    * Arrange to reschedule if the resulting priority is better
    * than that of the current process.
    */
   static void
   resetpriority(struct ksegrp *kg)
   {
           register unsigned int newpriority;
           struct thread *td;
   
           mtx_lock_spin(&sched_lock);
           if (kg->kg_pri_class == PRI_TIMESHARE) {
                   newpriority = PUSER + kg->kg_estcpu / INVERSE_ESTCPU_WEIGHT +
                       NICE_WEIGHT * (kg->kg_nice - PRIO_MIN);
                   newpriority = min(max(newpriority, PRI_MIN_TIMESHARE),
                       PRI_MAX_TIMESHARE);
                   kg->kg_user_pri = newpriority;
           }
           FOREACH_THREAD_IN_GROUP(kg, td) {
                   maybe_resched(td);                      /* XXXKSE silly */
           }
           mtx_unlock_spin(&sched_lock);
   }
   
   /* ARGSUSED */
   static void
   sched_setup(void *dummy)
   {
           if (sched_quantum == 0)
                   sched_quantum = SCHED_QUANTUM;
           hogticks = 2 * sched_quantum;
   
           callout_init(&schedcpu_callout, 1);
           callout_init(&roundrobin_callout, 0);
   
           /* Kick off timeout driven events by calling first time. */
           roundrobin(NULL);
           schedcpu(NULL);
   }
   
   /* External interfaces start here */
   int
   sched_runnable(void)
   {
           return runq_check(&runq);
   }
   
   int 
   sched_rr_interval(void)
   {
           if (sched_quantum == 0)
                   sched_quantum = SCHED_QUANTUM;
           return (sched_quantum);
   }
   
   /*
    * We adjust the priority of the current process.  The priority of
    * a process gets worse as it accumulates CPU time.  The cpu usage
    * estimator (p_estcpu) is increased here.  resetpriority() will
    * compute a different priority each time p_estcpu increases by
    * INVERSE_ESTCPU_WEIGHT
    * (until MAXPRI is reached).  The cpu usage estimator ramps up
    * quite quickly when the process is running (linearly), and decays
    * away exponentially, at a rate which is proportionally slower when
    * the system is busy.  The basic principle is that the system will
    * 90% forget that the process used a lot of CPU time in 5 * loadav
    * seconds.  This causes the system to favor processes which haven't
    * run much recently, and to round-robin among other processes.
    */
   void
   sched_clock(struct thread *td)
   {
           struct kse *ke;
           struct ksegrp *kg;
   
           KASSERT((td != NULL), ("schedclock: null thread pointer"));
           ke = td->td_kse;
           kg = td->td_ksegrp;
           ke->ke_cpticks++;
           kg->kg_estcpu = ESTCPULIM(kg->kg_estcpu + 1);
           if ((kg->kg_estcpu % INVERSE_ESTCPU_WEIGHT) == 0) {
                   resetpriority(kg);
                   if (td->td_priority >= PUSER)
                           td->td_priority = kg->kg_user_pri;
           }
   }
   /*
    * charge childs scheduling cpu usage to parent.
    *
    * XXXKSE assume only one thread & kse & ksegrp keep estcpu in each ksegrp.
    * Charge it to the ksegrp that did the wait since process estcpu is sum of
    * all ksegrps, this is strictly as expected.  Assume that the child process
    * aggregated all the estcpu into the 'built-in' ksegrp.
    */
   void
   sched_exit(struct ksegrp *kg, struct ksegrp *child)
   {
           kg->kg_estcpu = ESTCPULIM(kg->kg_estcpu + child->kg_estcpu);
   }
   
   void
   sched_fork(struct ksegrp *kg, struct ksegrp *child)
   {
           /*
            * set priority of child to be that of parent.
            * XXXKSE this needs redefining..
            */     
           child->kg_estcpu = kg->kg_estcpu;
   }
   
   void
   sched_nice(struct ksegrp *kg, int nice)
   {
           kg->kg_nice = nice;
           resetpriority(kg);
   }
   
   /*
    * Adjust the priority of a thread.
    * This may include moving the thread within the KSEGRP,
    * changing the assignment of a kse to the thread,
    * and moving a KSE in the system run queue.
    */
   void
   sched_prio(struct thread *td, u_char prio)
   {
   
           if (TD_ON_RUNQ(td)) {
                   adjustrunqueue(td, prio);
           } else {
                   td->td_priority = prio;
           }
   }
   
   void
   sched_sleep(struct thread *td, u_char prio)
   {
           td->td_ksegrp->kg_slptime = 0;
           td->td_priority = prio;
   }
   
   void
   sched_switchin(struct thread *td)
   {
           td->td_kse->ke_oncpu = PCPU_GET(cpuid);
   }
   
   void
   sched_switchout(struct thread *td)
   {
           struct kse *ke;
           struct proc *p;
   
           ke = td->td_kse;
           p = td->td_proc;
   
           KASSERT((ke->ke_state == KES_THREAD), ("mi_switch: kse state?"));
   
           td->td_lastcpu = ke->ke_oncpu;
           td->td_last_kse = ke;
           ke->ke_oncpu = NOCPU;
           ke->ke_flags &= ~KEF_NEEDRESCHED;
           /*
            * At the last moment, if this thread is still marked RUNNING,
            * then put it back on the run queue as it has not been suspended
            * or stopped or any thing else similar.
            */
           if (TD_IS_RUNNING(td)) {
                   /* Put us back on the run queue (kse and all). */
                   setrunqueue(td);
           } else if (p->p_flag & P_KSES) {
                   /*
                    * We will not be on the run queue. So we must be
                    * sleeping or similar. As it's available,
                    * someone else can use the KSE if they need it.
                    * (If bound LOANING can still occur).
                    */
                   kse_reassign(ke);
           }
   }
   
   void
   sched_wakeup(struct thread *td)
   {
           struct ksegrp *kg;
   
           kg = td->td_ksegrp;
           if (kg->kg_slptime > 1)
                   updatepri(kg);
           kg->kg_slptime = 0;
           setrunqueue(td);
           maybe_resched(td);
   }
   
   void
   sched_add(struct kse *ke)
   {
           mtx_assert(&sched_lock, MA_OWNED);
           KASSERT((ke->ke_thread != NULL), ("runq_add: No thread on KSE"));
           KASSERT((ke->ke_thread->td_kse != NULL),
               ("runq_add: No KSE on thread"));
           KASSERT(ke->ke_state != KES_ONRUNQ,
               ("runq_add: kse %p (%s) already in run queue", ke,
               ke->ke_proc->p_comm));
           KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
               ("runq_add: process swapped out"));
           ke->ke_ksegrp->kg_runq_kses++;
           ke->ke_state = KES_ONRUNQ;
   
           runq_add(&runq, ke);
   }
   
   void
   sched_rem(struct kse *ke)
   {
           KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
               ("runq_remove: process swapped out"));
           KASSERT((ke->ke_state == KES_ONRUNQ), ("KSE not on run queue"));
           mtx_assert(&sched_lock, MA_OWNED);
   
           runq_remove(&runq, ke);
           ke->ke_state = KES_THREAD;
           ke->ke_ksegrp->kg_runq_kses--;
   }
   
   struct kse *
   sched_choose(void)
   {
           struct kse *ke;
   
           ke = runq_choose(&runq);
   
           if (ke != NULL) {
                   runq_remove(&runq, ke);
                   ke->ke_state = KES_THREAD;
   
                   KASSERT((ke->ke_thread != NULL),
                       ("runq_choose: No thread on KSE"));
                   KASSERT((ke->ke_thread->td_kse != NULL),
                       ("runq_choose: No KSE on thread"));
                   KASSERT(ke->ke_proc->p_sflag & PS_INMEM,
                       ("runq_choose: process swapped out"));
           }
           return (ke);
   }
   
   void
   sched_userret(struct thread *td)
   {
           struct ksegrp *kg;
           /*
            * XXX we cheat slightly on the locking here to avoid locking in
            * the usual case.  Setting td_priority here is essentially an
            * incomplete workaround for not setting it properly elsewhere.
            * Now that some interrupt handlers are threads, not setting it
            * properly elsewhere can clobber it in the window between setting
            * it here and returning to user mode, so don't waste time setting
            * it perfectly here.
            */
           kg = td->td_ksegrp;
           if (td->td_priority != kg->kg_user_pri) {
                   mtx_lock_spin(&sched_lock);
                   td->td_priority = kg->kg_user_pri;
                   mtx_unlock_spin(&sched_lock);
           }
   }
   
   int
   sched_sizeof_kse(void)
   {
           return (sizeof(struct kse));
   }
   int
   sched_sizeof_ksegrp(void)
   {
           return (sizeof(struct ksegrp));
   }
   int
   sched_sizeof_proc(void)
   {
           return (sizeof(struct proc));
   }
   int
   sched_sizeof_thread(void)
   {
           return (sizeof(struct thread));
   }
   
   fixpt_t
   sched_pctcpu(struct kse *ke)
   {
           return (ke->ke_pctcpu);
   }

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