/* $OpenBSD: sched_bsd.c,v 1.17 2008/07/18 23:43:31 art Exp $ */ /* $NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $ */ /*- * 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. 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 8.6 (Berkeley) 1/21/94 */ #include #include #include #include #include #include #include #include #include #include #ifdef KTRACE #include #endif #include int lbolt; /* once a second sleep address */ int rrticks_init; /* # of hardclock ticks per roundrobin() */ #ifdef MULTIPROCESSOR struct __mp_lock sched_lock; #endif void scheduler_start(void); void roundrobin(struct cpu_info *); void schedcpu(void *); void updatepri(struct proc *); void endtsleep(void *); void scheduler_start(void) { static struct timeout schedcpu_to; /* * We avoid polluting the global namespace by keeping the scheduler * timeouts static in this function. * We setup the timeouts here and kick schedcpu and roundrobin once to * make them do their job. */ timeout_set(&schedcpu_to, schedcpu, &schedcpu_to); rrticks_init = hz / 10; schedcpu(&schedcpu_to); } /* * Force switch among equal priority processes every 100ms. */ void roundrobin(struct cpu_info *ci) { struct schedstate_percpu *spc = &ci->ci_schedstate; int s; spc->spc_rrticks = rrticks_init; if (curproc != NULL) { s = splstatclock(); if (spc->spc_schedflags & SPCF_SEENRR) { /* * The process has already been through a roundrobin * without switching and may be hogging the CPU. * Indicate that the process should yield. */ spc->spc_schedflags |= SPCF_SHOULDYIELD; } else { spc->spc_schedflags |= SPCF_SEENRR; } splx(s); } need_resched(curcpu()); } /* * 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 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. */ void schedcpu(void *arg) { struct timeout *to = (struct timeout *)arg; fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); struct proc *p; int s; unsigned int newcpu; int phz; /* * If we have a statistics clock, use that to calculate CPU * time, otherwise revert to using the profiling clock (which, * in turn, defaults to hz if there is no separate profiling * clock available) */ phz = stathz ? stathz : profhz; KASSERT(phz); LIST_FOREACH(p, &allproc, p_list) { /* * 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; SCHED_LOCK(s); /* * p_pctcpu is only for ps. */ #if (FSHIFT >= CCPU_SHIFT) p->p_pctcpu += (phz == 100)? ((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT): 100 * (((fixpt_t) p->p_cpticks) << (FSHIFT - CCPU_SHIFT)) / phz; #else p->p_pctcpu += ((FSCALE - ccpu) * (p->p_cpticks * FSCALE / phz)) >> 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_priority / PPQ) != (p->p_usrpri / PPQ)) { remrunqueue(p); p->p_priority = p->p_usrpri; setrunqueue(p); } else p->p_priority = p->p_usrpri; } SCHED_UNLOCK(s); } uvm_meter(); wakeup(&lbolt); timeout_add(to, 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(struct proc *p) { unsigned int newcpu = p->p_estcpu; fixpt_t loadfac = loadfactor(averunnable.ldavg[0]); SCHED_ASSERT_LOCKED(); 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); } /* * General yield call. Puts the current process back on its run queue and * performs a voluntary context switch. */ void yield(void) { struct proc *p = curproc; int s; SCHED_LOCK(s); p->p_priority = p->p_usrpri; p->p_stat = SRUN; setrunqueue(p); p->p_stats->p_ru.ru_nvcsw++; mi_switch(); SCHED_UNLOCK(s); } /* * General preemption call. Puts the current process back on its run queue * and performs an involuntary context switch. If a process is supplied, * we switch to that process. Otherwise, we use the normal process selection * criteria. */ void preempt(struct proc *newp) { struct proc *p = curproc; int s; /* * XXX Switching to a specific process is not supported yet. */ if (newp != NULL) panic("preempt: cpu_preempt not yet implemented"); SCHED_LOCK(s); p->p_priority = p->p_usrpri; p->p_stat = SRUN; setrunqueue(p); p->p_stats->p_ru.ru_nivcsw++; mi_switch(); SCHED_UNLOCK(s); } void mi_switch(void) { struct schedstate_percpu *spc = &curcpu()->ci_schedstate; struct proc *p = curproc; struct proc *nextproc; struct rlimit *rlim; struct timeval tv; #ifdef MULTIPROCESSOR int hold_count; int sched_count; #endif KASSERT(p->p_stat != SONPROC); SCHED_ASSERT_LOCKED(); #ifdef MULTIPROCESSOR /* * Release the kernel_lock, as we are about to yield the CPU. */ sched_count = __mp_release_all_but_one(&sched_lock); if (p->p_flag & P_BIGLOCK) hold_count = __mp_release_all(&kernel_lock); #endif /* * Compute the amount of time during which the current * process was running, and add that to its total so far. */ microuptime(&tv); if (timercmp(&tv, &spc->spc_runtime, <)) { #if 0 printf("uptime is not monotonic! " "tv=%lu.%06lu, runtime=%lu.%06lu\n", tv.tv_sec, tv.tv_usec, spc->spc_runtime.tv_sec, spc->spc_runtime.tv_usec); #endif } else { timersub(&tv, &spc->spc_runtime, &tv); timeradd(&p->p_rtime, &tv, &p->p_rtime); } /* * Check if the process exceeds its cpu resource allocation. * If over max, kill it. */ rlim = &p->p_rlimit[RLIMIT_CPU]; if ((rlim_t)p->p_rtime.tv_sec >= rlim->rlim_cur) { if ((rlim_t)p->p_rtime.tv_sec >= rlim->rlim_max) { psignal(p, SIGKILL); } else { psignal(p, SIGXCPU); if (rlim->rlim_cur < rlim->rlim_max) rlim->rlim_cur += 5; } } /* * Process is about to yield the CPU; clear the appropriate * scheduling flags. */ spc->spc_schedflags &= ~SPCF_SWITCHCLEAR; nextproc = sched_chooseproc(); if (p != nextproc) { uvmexp.swtch++; cpu_switchto(p, nextproc); } else { p->p_stat = SONPROC; } clear_resched(curcpu()); SCHED_ASSERT_LOCKED(); /* * To preserve lock ordering, we need to release the sched lock * and grab it after we grab the big lock. * In the future, when the sched lock isn't recursive, we'll * just release it here. */ #ifdef MULTIPROCESSOR __mp_unlock(&sched_lock); #endif SCHED_ASSERT_UNLOCKED(); /* * We're running again; record our new start time. We might * be running on a new CPU now, so don't use the cache'd * schedstate_percpu pointer. */ KASSERT(p->p_cpu == curcpu()); microuptime(&p->p_cpu->ci_schedstate.spc_runtime); #ifdef MULTIPROCESSOR /* * Reacquire the kernel_lock now. We do this after we've * released the scheduler lock to avoid deadlock, and before * we reacquire the interlock and the scheduler lock. */ if (p->p_flag & P_BIGLOCK) __mp_acquire_count(&kernel_lock, hold_count); __mp_acquire_count(&sched_lock, sched_count + 1); #endif } static __inline void resched_proc(struct proc *p, u_char pri) { struct cpu_info *ci; /* * XXXSMP * Since p->p_cpu persists across a context switch, * this gives us *very weak* processor affinity, in * that we notify the CPU on which the process last * ran that it should try to switch. * * This does not guarantee that the process will run on * that processor next, because another processor might * grab it the next time it performs a context switch. * * This also does not handle the case where its last * CPU is running a higher-priority process, but every * other CPU is running a lower-priority process. There * are ways to handle this situation, but they're not * currently very pretty, and we also need to weigh the * cost of moving a process from one CPU to another. * * XXXSMP * There is also the issue of locking the other CPU's * sched state, which we currently do not do. */ ci = (p->p_cpu != NULL) ? p->p_cpu : curcpu(); if (pri < ci->ci_schedstate.spc_curpriority) need_resched(ci); } /* * 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(struct proc *p) { SCHED_ASSERT_LOCKED(); switch (p->p_stat) { case 0: case SRUN: case SONPROC: 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) atomic_setbits_int(&p->p_siglist, sigmask(p->p_xstat)); case SSLEEP: unsleep(p); /* e.g. when sending signals */ break; case SIDL: break; } p->p_stat = SRUN; setrunqueue(p); if (p->p_slptime > 1) updatepri(p); p->p_slptime = 0; resched_proc(p, p->p_priority); } /* * 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(struct proc *p) { unsigned int newpriority; SCHED_ASSERT_LOCKED(); newpriority = PUSER + p->p_estcpu + NICE_WEIGHT * (p->p_nice - NZERO); newpriority = min(newpriority, MAXPRI); p->p_usrpri = newpriority; resched_proc(p, p->p_usrpri); } /* * 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 * 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 schedclock(struct proc *p) { int s; SCHED_LOCK(s); p->p_estcpu = ESTCPULIM(p->p_estcpu + 1); resetpriority(p); if (p->p_priority >= PUSER) p->p_priority = p->p_usrpri; SCHED_UNLOCK(s); }