/* $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);
}