/* $NetBSD: kern_synch.c,v 1.63 1999/07/26 23:00:59 thorpej Exp $ */ /*- * Copyright (c) 1999 The NetBSD Foundation, Inc. * All rights reserved. * * This code is derived from software contributed to The NetBSD Foundation * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility, * NASA Ames Research Center. * * 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 NetBSD * Foundation, Inc. and its contributors. * 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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. */ /*- * 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. * * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 */ #include "opt_ddb.h" #include "opt_ktrace.h" #include #include #include #include #include #include #include #include #include #include #ifdef KTRACE #include #endif #define NICE_WEIGHT 2 /* priorities per nice level */ #define PPQ (128 / NQS) /* priorities per queue */ #define ESTCPULIM(e) min((e), NICE_WEIGHT * PRIO_MAX - PPQ) #include u_char curpriority; /* usrpri of curproc */ int lbolt; /* once a second sleep address */ void roundrobin __P((void *)); void schedcpu __P((void *)); void updatepri __P((struct proc *)); void endtsleep __P((void *)); __inline void awaken __P((struct proc *)); /* * Force switch among equal priority processes every 100ms. */ /* ARGSUSED */ void roundrobin(arg) void *arg; { need_resched(); timeout(roundrobin, NULL, hz / 10); } /* * 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 hardclock updates p_estcpu and p_cpticks independently. * * 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 */ fixpt_t ccpu = 0.95122942450071400909 * FSCALE; /* exp(-1/20) */ /* * 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 dont 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. */ /* ARGSUSED */ void schedcpu(arg) void *arg; { register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); register struct proc *p; register int s; register unsigned int newcpu; wakeup((caddr_t)&lbolt); proclist_lock_read(); for (p = allproc.lh_first; p != 0; p = p->p_list.le_next) { /* * 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. */ p->p_swtime++; if (p->p_stat == SSLEEP || p->p_stat == SSTOP) p->p_slptime++; p->p_pctcpu = (p->p_pctcpu * ccpu) >> FSHIFT; /* * If the process has slept the entire second, * stop recalculating its priority until it wakes up. */ if (p->p_slptime > 1) continue; s = splstatclock(); /* prevent state changes */ /* * p_pctcpu is only for ps. */ KASSERT(profhz); #if (FSHIFT >= CCPU_SHIFT) p->p_pctcpu += (profhz == 100)? ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT): 100 * (((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT)) / profhz; #else p->p_pctcpu += ((FSCALE - ccpu) * (p->p_cpticks * FSCALE / profhz)) >> FSHIFT; #endif p->p_cpticks = 0; newcpu = (u_int)decay_cpu(loadfac, p->p_estcpu); p->p_estcpu = newcpu; resetpriority(p); if (p->p_priority >= PUSER) { if ((p != curproc) && p->p_stat == SRUN && (p->p_flag & P_INMEM) && (p->p_priority / PPQ) != (p->p_usrpri / PPQ)) { remrunqueue(p); p->p_priority = p->p_usrpri; setrunqueue(p); } else p->p_priority = p->p_usrpri; } splx(s); } proclist_unlock_read(); uvm_meter(); timeout(schedcpu, (void *)0, hz); } /* * 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. */ void updatepri(p) register struct proc *p; { register unsigned int newcpu = p->p_estcpu; register fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); if (p->p_slptime > 5 * loadfac) p->p_estcpu = 0; else { p->p_slptime--; /* the first time was done in schedcpu */ while (newcpu && --p->p_slptime) newcpu = (int) decay_cpu(loadfac, newcpu); p->p_estcpu = newcpu; } resetpriority(p); } /* * We're only looking at 7 bits of the address; everything is * aligned to 4, lots of things are aligned to greater powers * of 2. Shift right by 8, i.e. drop the bottom 256 worth. */ #define TABLESIZE 128 #define LOOKUP(x) (((long)(x) >> 8) & (TABLESIZE - 1)) struct slpque { struct proc *sq_head; struct proc **sq_tailp; } slpque[TABLESIZE]; /* * During autoconfiguration or after a panic, a sleep will simply * lower the priority briefly to allow interrupts, then return. * The priority to be used (safepri) is machine-dependent, thus this * value is initialized and maintained in the machine-dependent layers. * This priority will typically be 0, or the lowest priority * that is safe for use on the interrupt stack; it can be made * higher to block network software interrupts after panics. */ int safepri; /* * General sleep call. Suspends the current process until a wakeup is * performed on the specified identifier. The process will then be made * runnable with the specified priority. Sleeps at most timo/hz seconds * (0 means no timeout). If pri includes PCATCH flag, signals are checked * before and after sleeping, else signals are not checked. Returns 0 if * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a * signal needs to be delivered, ERESTART is returned if the current system * call should be restarted if possible, and EINTR is returned if the system * call should be interrupted by the signal (return EINTR). */ int tsleep(ident, priority, wmesg, timo) void *ident; int priority, timo; const char *wmesg; { register struct proc *p = curproc; register struct slpque *qp; register int s; int sig, catch = priority & PCATCH; extern int cold; void endtsleep __P((void *)); if (cold || panicstr) { /* * After a panic, or during autoconfiguration, * just give interrupts a chance, then just return; * don't run any other procs or panic below, * in case this is the idle process and already asleep. */ s = splhigh(); splx(safepri); splx(s); return (0); } #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 1, 0); #endif s = splhigh(); #ifdef DIAGNOSTIC if (ident == NULL || p->p_stat != SRUN || p->p_back) panic("tsleep"); #endif p->p_wchan = ident; p->p_wmesg = wmesg; p->p_slptime = 0; p->p_priority = priority & PRIMASK; qp = &slpque[LOOKUP(ident)]; if (qp->sq_head == 0) qp->sq_head = p; else *qp->sq_tailp = p; *(qp->sq_tailp = &p->p_forw) = 0; if (timo) timeout(endtsleep, (void *)p, timo); /* * We put ourselves on the sleep queue and start our timeout * before calling CURSIG, as we could stop there, and a wakeup * or a SIGCONT (or both) could occur while we were stopped. * A SIGCONT would cause us to be marked as SSLEEP * without resuming us, thus we must be ready for sleep * when CURSIG is called. If the wakeup happens while we're * stopped, p->p_wchan will be 0 upon return from CURSIG. */ if (catch) { p->p_flag |= P_SINTR; if ((sig = CURSIG(p)) != 0) { if (p->p_wchan) unsleep(p); p->p_stat = SRUN; goto resume; } if (p->p_wchan == 0) { catch = 0; goto resume; } } else sig = 0; p->p_stat = SSLEEP; p->p_stats->p_ru.ru_nvcsw++; mi_switch(); #ifdef DDB /* handy breakpoint location after process "wakes" */ asm(".globl bpendtsleep ; bpendtsleep:"); #endif resume: curpriority = p->p_usrpri; splx(s); p->p_flag &= ~P_SINTR; if (p->p_flag & P_TIMEOUT) { p->p_flag &= ~P_TIMEOUT; if (sig == 0) { #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 0, 0); #endif return (EWOULDBLOCK); } } else if (timo) untimeout(endtsleep, (void *)p); if (catch && (sig != 0 || (sig = CURSIG(p)) != 0)) { #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 0, 0); #endif if ((p->p_sigacts->ps_sigact[sig].sa_flags & SA_RESTART) == 0) return (EINTR); return (ERESTART); } #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 0, 0); #endif return (0); } /* * Implement timeout for tsleep. * If process hasn't been awakened (wchan non-zero), * set timeout flag and undo the sleep. If proc * is stopped, just unsleep so it will remain stopped. */ void endtsleep(arg) void *arg; { register struct proc *p; int s; p = (struct proc *)arg; s = splhigh(); if (p->p_wchan) { if (p->p_stat == SSLEEP) setrunnable(p); else unsleep(p); p->p_flag |= P_TIMEOUT; } splx(s); } /* * Short-term, non-interruptable sleep. */ void sleep(ident, priority) void *ident; int priority; { register struct proc *p = curproc; register struct slpque *qp; register int s; extern int cold; #ifdef DIAGNOSTIC if (priority > PZERO) { printf("sleep called with priority %d > PZERO, wchan: %p\n", priority, ident); panic("old sleep"); } #endif s = splhigh(); if (cold || panicstr) { /* * After a panic, or during autoconfiguration, * just give interrupts a chance, then just return; * don't run any other procs or panic below, * in case this is the idle process and already asleep. */ splx(safepri); splx(s); return; } #ifdef DIAGNOSTIC if (ident == NULL || p->p_stat != SRUN || p->p_back) panic("sleep"); #endif p->p_wchan = ident; p->p_wmesg = NULL; p->p_slptime = 0; p->p_priority = priority; qp = &slpque[LOOKUP(ident)]; if (qp->sq_head == 0) qp->sq_head = p; else *qp->sq_tailp = p; *(qp->sq_tailp = &p->p_forw) = 0; p->p_stat = SSLEEP; p->p_stats->p_ru.ru_nvcsw++; #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 1, 0); #endif mi_switch(); #ifdef DDB /* handy breakpoint location after process "wakes" */ asm(".globl bpendsleep ; bpendsleep:"); #endif #ifdef KTRACE if (KTRPOINT(p, KTR_CSW)) ktrcsw(p->p_tracep, 0, 0); #endif curpriority = p->p_usrpri; splx(s); } /* * Remove a process from its wait queue */ void unsleep(p) register struct proc *p; { register struct slpque *qp; register struct proc **hp; int s; s = splhigh(); if (p->p_wchan) { hp = &(qp = &slpque[LOOKUP(p->p_wchan)])->sq_head; while (*hp != p) hp = &(*hp)->p_forw; *hp = p->p_forw; if (qp->sq_tailp == &p->p_forw) qp->sq_tailp = hp; p->p_wchan = 0; } splx(s); } /* * Optimized-for-wakeup() version of setrunnable(). */ __inline void awaken(p) struct proc *p; { if (p->p_slptime > 1) updatepri(p); p->p_slptime = 0; p->p_stat = SRUN; /* * Since curpriority is a user priority, p->p_priority * is always better than curpriority. */ if (p->p_flag & P_INMEM) { setrunqueue(p); need_resched(); } else wakeup((caddr_t)&proc0); } /* * Make all processes sleeping on the specified identifier runnable. */ void wakeup(ident) register void *ident; { register struct slpque *qp; register struct proc *p, **q; int s; s = splhigh(); qp = &slpque[LOOKUP(ident)]; restart: for (q = &qp->sq_head; (p = *q) != NULL; ) { #ifdef DIAGNOSTIC if (p->p_back || (p->p_stat != SSLEEP && p->p_stat != SSTOP)) panic("wakeup"); #endif if (p->p_wchan == ident) { p->p_wchan = 0; *q = p->p_forw; if (qp->sq_tailp == &p->p_forw) qp->sq_tailp = q; if (p->p_stat == SSLEEP) { awaken(p); goto restart; } } else q = &p->p_forw; } splx(s); } /* * Make the highest priority process first in line on the specified * identifier runnable. */ void wakeup_one(ident) void *ident; { struct slpque *qp; struct proc *p, **q; struct proc *best_sleepp, **best_sleepq; struct proc *best_stopp, **best_stopq; int s; best_sleepp = best_stopp = NULL; best_sleepq = best_stopq = NULL; s = splhigh(); qp = &slpque[LOOKUP(ident)]; for (q = &qp->sq_head; (p = *q) != NULL; q = &p->p_forw) { #ifdef DIAGNOSTIC if (p->p_back || (p->p_stat != SSLEEP && p->p_stat != SSTOP)) panic("wakeup_one"); #endif if (p->p_wchan == ident) { if (p->p_stat == SSLEEP) { if (best_sleepp == NULL || p->p_priority < best_sleepp->p_priority) { best_sleepp = p; best_sleepq = q; } } else { if (best_stopp == NULL || p->p_priority < best_stopp->p_priority) { best_stopp = p; best_stopq = q; } } } } /* * Consider any SSLEEP process higher than the highest priority SSTOP * process. */ if (best_sleepp != NULL) { p = best_sleepp; q = best_sleepq; } else { p = best_stopp; q = best_stopq; } if (p != NULL) { p->p_wchan = 0; *q = p->p_forw; if (qp->sq_tailp == &p->p_forw) qp->sq_tailp = q; if (p->p_stat == SSLEEP) awaken(p); } splx(s); } /* * The machine independent parts of mi_switch(). * Must be called at splstatclock() or higher. */ void mi_switch() { register struct proc *p = curproc; /* XXX */ register struct rlimit *rlim; register long s, u; struct timeval tv; #ifdef DEBUG if (p->p_simple_locks) { printf("p->p_simple_locks %d\n", p->p_simple_locks); #ifdef LOCKDEBUG simple_lock_dump(); #endif panic("sleep: holding simple lock"); } #endif /* * Compute the amount of time during which the current * process was running, and add that to its total so far. */ microtime(&tv); u = p->p_rtime.tv_usec + (tv.tv_usec - runtime.tv_usec); s = p->p_rtime.tv_sec + (tv.tv_sec - runtime.tv_sec); if (u < 0) { u += 1000000; s--; } else if (u >= 1000000) { u -= 1000000; s++; } p->p_rtime.tv_usec = u; p->p_rtime.tv_sec = s; /* * Check if the process exceeds its cpu resource allocation. * If over max, kill it. In any case, if it has run for more * than 10 minutes, reduce priority to give others a chance. */ rlim = &p->p_rlimit[RLIMIT_CPU]; if (s >= rlim->rlim_cur) { if (s >= rlim->rlim_max) psignal(p, SIGKILL); else { psignal(p, SIGXCPU); if (rlim->rlim_cur < rlim->rlim_max) rlim->rlim_cur += 5; } } if (autonicetime && s > autonicetime && p->p_ucred->cr_uid && p->p_nice == NZERO) { p->p_nice = autoniceval + NZERO; resetpriority(p); } /* * Pick a new current process and record its start time. */ uvmexp.swtch++; cpu_switch(p); microtime(&runtime); } /* * Initialize the (doubly-linked) run queues * to be empty. */ void rqinit() { register int i; for (i = 0; i < NQS; i++) qs[i].ph_link = qs[i].ph_rlink = (struct proc *)&qs[i]; } /* * Change process state to be runnable, * placing it on the run queue if it is in memory, * and awakening the swapper if it isn't in memory. */ void setrunnable(p) register struct proc *p; { register int s; s = splhigh(); switch (p->p_stat) { case 0: case SRUN: case SZOMB: case SDEAD: default: panic("setrunnable"); case SSTOP: /* * If we're being traced (possibly because someone attached us * while we were stopped), check for a signal from the debugger. */ if ((p->p_flag & P_TRACED) != 0 && p->p_xstat != 0) { sigaddset(&p->p_siglist, p->p_xstat); p->p_sigcheck = 1; } case SSLEEP: unsleep(p); /* e.g. when sending signals */ break; case SIDL: break; } p->p_stat = SRUN; if (p->p_flag & P_INMEM) setrunqueue(p); splx(s); if (p->p_slptime > 1) updatepri(p); p->p_slptime = 0; if ((p->p_flag & P_INMEM) == 0) wakeup((caddr_t)&proc0); else if (p->p_priority < curpriority) need_resched(); } /* * 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. */ void resetpriority(p) register struct proc *p; { register unsigned int newpriority; newpriority = PUSER + p->p_estcpu + NICE_WEIGHT * (p->p_nice - NZERO); newpriority = min(newpriority, MAXPRI); p->p_usrpri = newpriority; if (newpriority < curpriority) need_resched(); } /* * 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. The formula for computing priorities (in kern_synch.c) * will compute a different value each time p_estcpu increases. This can * cause a switch, but unless the priority crosses a PPQ boundary the actual * queue will not change. 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 * principal 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 schedclock(p) struct proc *p; { p->p_estcpu = ESTCPULIM(p->p_estcpu + 1); resetpriority(p); if (p->p_priority >= PUSER) p->p_priority = p->p_usrpri; }