freebsd-nq/sys/kern/kern_synch.c
Bruce M Simpson 0c9601bc6b Add a pre-emption counter, td_generation, so that threads can notice
when they have been pre-empted by other threads. This is bumped from
within mi_switch() every time a context switch takes place.

Discussed with:	pete
2003-10-05 09:35:08 +00:00

674 lines
18 KiB
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.
*
* @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_ddb.h"
#include "opt_ktrace.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/condvar.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/signalvar.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/vmmeter.h>
#ifdef DDB
#include <ddb/ddb.h>
#endif
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <machine/cpu.h>
static void sched_setup(void *dummy);
SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL)
int hogticks;
int lbolt;
static struct callout loadav_callout;
static struct callout lbolt_callout;
struct loadavg averunnable =
{ {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
/*
* Constants for averages over 1, 5, and 15 minutes
* when sampling at 5 second intervals.
*/
static fixpt_t cexp[3] = {
0.9200444146293232 * FSCALE, /* exp(-1/12) */
0.9834714538216174 * FSCALE, /* exp(-1/60) */
0.9944598480048967 * FSCALE, /* exp(-1/180) */
};
/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
static int fscale __unused = FSCALE;
SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
static void endtsleep(void *);
static void loadav(void *arg);
static void lboltcb(void *arg);
/*
* 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
static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE];
#define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1))
void
sleepinit(void)
{
int i;
hogticks = (hz / 10) * 2; /* Default only. */
for (i = 0; i < TABLESIZE; i++)
TAILQ_INIT(&slpque[i]);
}
/*
* 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).
*
* The mutex argument is exited before the caller is suspended, and
* entered before msleep returns. If priority includes the PDROP
* flag the mutex is not entered before returning.
*/
int
msleep(ident, mtx, priority, wmesg, timo)
void *ident;
struct mtx *mtx;
int priority, timo;
const char *wmesg;
{
struct thread *td = curthread;
struct proc *p = td->td_proc;
int sig, catch = priority & PCATCH;
int rval = 0;
WITNESS_SAVE_DECL(mtx);
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(1, 0);
#endif
/* XXX: mtx == NULL ?? */
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, &mtx->mtx_object,
"Sleeping on \"%s\"", wmesg);
KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL,
("sleeping without a mutex"));
/*
* If we are capable of async syscalls and there isn't already
* another one ready to return, start a new thread
* and queue it as ready to run. Note that there is danger here
* because we need to make sure that we don't sleep allocating
* the thread (recursion here might be bad).
*/
mtx_lock_spin(&sched_lock);
if (p->p_flag & P_SA || p->p_numthreads > 1) {
/*
* Just don't bother if we are exiting
* and not the exiting thread or thread was marked as
* interrupted.
*/
if (catch) {
if ((p->p_flag & P_WEXIT) && p->p_singlethread != td) {
mtx_unlock_spin(&sched_lock);
return (EINTR);
}
if (td->td_flags & TDF_INTERRUPT) {
mtx_unlock_spin(&sched_lock);
return (td->td_intrval);
}
}
}
if (cold ) {
/*
* During autoconfiguration, just return;
* don't run any other procs or panic below,
* in case this is the idle process and already asleep.
* XXX: this used to do "s = splhigh(); splx(safepri);
* splx(s);" to give interrupts a chance, but there is
* no way to give interrupts a chance now.
*/
if (mtx != NULL && priority & PDROP)
mtx_unlock(mtx);
mtx_unlock_spin(&sched_lock);
return (0);
}
DROP_GIANT();
if (mtx != NULL) {
mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
WITNESS_SAVE(&mtx->mtx_object, mtx);
mtx_unlock(mtx);
if (priority & PDROP)
mtx = NULL;
}
KASSERT(p != NULL, ("msleep1"));
KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
CTR5(KTR_PROC, "msleep: thread %p (pid %d, %s) on %s (%p)",
td, p->p_pid, p->p_comm, wmesg, ident);
td->td_wchan = ident;
td->td_wmesg = wmesg;
TAILQ_INSERT_TAIL(&slpque[LOOKUP(ident)], td, td_slpq);
TD_SET_ON_SLEEPQ(td);
if (timo)
callout_reset(&td->td_slpcallout, timo, endtsleep, td);
/*
* We put ourselves on the sleep queue and start our timeout
* before calling thread_suspend_check, as we could stop there, and
* a wakeup or a SIGCONT (or both) could occur while we were stopped.
* without resuming us, thus we must be ready for sleep
* when cursig is called. If the wakeup happens while we're
* stopped, td->td_wchan will be 0 upon return from cursig.
*/
if (catch) {
CTR3(KTR_PROC, "msleep caught: thread %p (pid %d, %s)", td,
p->p_pid, p->p_comm);
td->td_flags |= TDF_SINTR;
mtx_unlock_spin(&sched_lock);
PROC_LOCK(p);
mtx_lock(&p->p_sigacts->ps_mtx);
sig = cursig(td);
mtx_unlock(&p->p_sigacts->ps_mtx);
if (sig == 0 && thread_suspend_check(1))
sig = SIGSTOP;
mtx_lock_spin(&sched_lock);
PROC_UNLOCK(p);
if (sig != 0) {
if (TD_ON_SLEEPQ(td))
unsleep(td);
} else if (!TD_ON_SLEEPQ(td))
catch = 0;
} else
sig = 0;
/*
* Let the scheduler know we're about to voluntarily go to sleep.
*/
sched_sleep(td, priority & PRIMASK);
if (TD_ON_SLEEPQ(td)) {
p->p_stats->p_ru.ru_nvcsw++;
TD_SET_SLEEPING(td);
mi_switch();
}
/*
* We're awake from voluntary sleep.
*/
CTR3(KTR_PROC, "msleep resume: thread %p (pid %d, %s)", td, p->p_pid,
p->p_comm);
KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
td->td_flags &= ~TDF_SINTR;
if (td->td_flags & TDF_TIMEOUT) {
td->td_flags &= ~TDF_TIMEOUT;
if (sig == 0)
rval = EWOULDBLOCK;
} else if (td->td_flags & TDF_TIMOFAIL) {
td->td_flags &= ~TDF_TIMOFAIL;
} else if (timo && callout_stop(&td->td_slpcallout) == 0) {
/*
* This isn't supposed to be pretty. If we are here, then
* the endtsleep() callout is currently executing on another
* CPU and is either spinning on the sched_lock or will be
* soon. If we don't synchronize here, there is a chance
* that this process may msleep() again before the callout
* has a chance to run and the callout may end up waking up
* the wrong msleep(). Yuck.
*/
TD_SET_SLEEPING(td);
p->p_stats->p_ru.ru_nivcsw++;
mi_switch();
td->td_flags &= ~TDF_TIMOFAIL;
}
if ((td->td_flags & TDF_INTERRUPT) && (priority & PCATCH) &&
(rval == 0)) {
rval = td->td_intrval;
}
mtx_unlock_spin(&sched_lock);
if (rval == 0 && catch) {
PROC_LOCK(p);
/* XXX: shouldn't we always be calling cursig()? */
mtx_lock(&p->p_sigacts->ps_mtx);
if (sig != 0 || (sig = cursig(td))) {
if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
rval = EINTR;
else
rval = ERESTART;
}
mtx_unlock(&p->p_sigacts->ps_mtx);
PROC_UNLOCK(p);
}
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(0, 0);
#endif
PICKUP_GIANT();
if (mtx != NULL) {
mtx_lock(mtx);
WITNESS_RESTORE(&mtx->mtx_object, mtx);
}
return (rval);
}
/*
* Implement timeout for msleep().
*
* 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.
* MP-safe, called without the Giant mutex.
*/
static void
endtsleep(arg)
void *arg;
{
register struct thread *td;
td = (struct thread *)arg;
CTR3(KTR_PROC, "endtsleep: thread %p (pid %d, %s)",
td, td->td_proc->p_pid, td->td_proc->p_comm);
mtx_lock_spin(&sched_lock);
/*
* This is the other half of the synchronization with msleep()
* described above. If the TDS_TIMEOUT flag is set, we lost the
* race and just need to put the process back on the runqueue.
*/
if (TD_ON_SLEEPQ(td)) {
TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq);
TD_CLR_ON_SLEEPQ(td);
td->td_flags |= TDF_TIMEOUT;
td->td_wmesg = NULL;
} else
td->td_flags |= TDF_TIMOFAIL;
TD_CLR_SLEEPING(td);
setrunnable(td);
mtx_unlock_spin(&sched_lock);
}
/*
* Abort a thread, as if an interrupt had occured. Only abort
* interruptable waits (unfortunatly it isn't only safe to abort others).
* This is about identical to cv_abort().
* Think about merging them?
* Also, whatever the signal code does...
*/
void
abortsleep(struct thread *td)
{
mtx_assert(&sched_lock, MA_OWNED);
/*
* If the TDF_TIMEOUT flag is set, just leave. A
* timeout is scheduled anyhow.
*/
if ((td->td_flags & (TDF_TIMEOUT | TDF_SINTR)) == TDF_SINTR) {
if (TD_ON_SLEEPQ(td)) {
unsleep(td);
TD_CLR_SLEEPING(td);
setrunnable(td);
}
}
}
/*
* Remove a process from its wait queue
*/
void
unsleep(struct thread *td)
{
mtx_lock_spin(&sched_lock);
if (TD_ON_SLEEPQ(td)) {
TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq);
TD_CLR_ON_SLEEPQ(td);
td->td_wmesg = NULL;
}
mtx_unlock_spin(&sched_lock);
}
/*
* Make all processes sleeping on the specified identifier runnable.
*/
void
wakeup(ident)
register void *ident;
{
register struct slpquehead *qp;
register struct thread *td;
struct thread *ntd;
struct proc *p;
mtx_lock_spin(&sched_lock);
qp = &slpque[LOOKUP(ident)];
restart:
for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
ntd = TAILQ_NEXT(td, td_slpq);
if (td->td_wchan == ident) {
unsleep(td);
TD_CLR_SLEEPING(td);
setrunnable(td);
p = td->td_proc;
CTR3(KTR_PROC,"wakeup: thread %p (pid %d, %s)",
td, p->p_pid, p->p_comm);
goto restart;
}
}
mtx_unlock_spin(&sched_lock);
}
/*
* Make a process sleeping on the specified identifier runnable.
* May wake more than one process if a target process is currently
* swapped out.
*/
void
wakeup_one(ident)
register void *ident;
{
register struct proc *p;
register struct slpquehead *qp;
register struct thread *td;
struct thread *ntd;
mtx_lock_spin(&sched_lock);
qp = &slpque[LOOKUP(ident)];
for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
ntd = TAILQ_NEXT(td, td_slpq);
if (td->td_wchan == ident) {
unsleep(td);
TD_CLR_SLEEPING(td);
setrunnable(td);
p = td->td_proc;
CTR3(KTR_PROC,"wakeup1: thread %p (pid %d, %s)",
td, p->p_pid, p->p_comm);
break;
}
}
mtx_unlock_spin(&sched_lock);
}
/*
* The machine independent parts of mi_switch().
*/
void
mi_switch(void)
{
struct bintime new_switchtime;
struct thread *td;
struct thread *newtd;
struct proc *p;
u_int sched_nest;
mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
td = curthread; /* XXX */
p = td->td_proc; /* XXX */
KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
#ifdef INVARIANTS
if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
mtx_assert(&Giant, MA_NOTOWNED);
#endif
KASSERT(td->td_critnest == 1,
("mi_switch: switch in a critical section"));
/*
* Compute the amount of time during which the current
* process was running, and add that to its total so far.
*/
binuptime(&new_switchtime);
bintime_add(&p->p_runtime, &new_switchtime);
bintime_sub(&p->p_runtime, PCPU_PTR(switchtime));
td->td_generation++; /* bump preempt-detect counter */
#ifdef DDB
/*
* Don't perform context switches from the debugger.
*/
if (db_active) {
mtx_unlock_spin(&sched_lock);
db_print_backtrace();
db_error("Context switches not allowed in the debugger");
}
#endif
/*
* Check if the process exceeds its cpu resource allocation. If
* over max, arrange to kill the process in ast().
*/
if (p->p_cpulimit != RLIM_INFINITY &&
p->p_runtime.sec > p->p_cpulimit) {
p->p_sflag |= PS_XCPU;
td->td_flags |= TDF_ASTPENDING;
}
/*
* Finish up stats for outgoing thread.
*/
cnt.v_swtch++;
PCPU_SET(switchtime, new_switchtime);
CTR3(KTR_PROC, "mi_switch: old thread %p (pid %d, %s)", td, p->p_pid,
p->p_comm);
sched_nest = sched_lock.mtx_recurse;
if (td->td_proc->p_flag & P_SA)
thread_switchout(td);
sched_switchout(td);
newtd = choosethread();
if (td != newtd)
cpu_switch(td, newtd); /* SHAZAM!! */
sched_lock.mtx_recurse = sched_nest;
sched_lock.mtx_lock = (uintptr_t)td;
sched_switchin(td);
/*
* Start setting up stats etc. for the incoming thread.
* Similar code in fork_exit() is returned to by cpu_switch()
* in the case of a new thread/process.
*/
CTR3(KTR_PROC, "mi_switch: new thread %p (pid %d, %s)", td, p->p_pid,
p->p_comm);
if (PCPU_GET(switchtime.sec) == 0)
binuptime(PCPU_PTR(switchtime));
PCPU_SET(switchticks, ticks);
/*
* If the last thread was exiting, finish cleaning it up.
*/
if ((td = PCPU_GET(deadthread))) {
PCPU_SET(deadthread, NULL);
thread_stash(td);
}
}
/*
* 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 thread *td)
{
struct proc *p;
p = td->td_proc;
mtx_assert(&sched_lock, MA_OWNED);
switch (p->p_state) {
case PRS_ZOMBIE:
panic("setrunnable(1)");
default:
break;
}
switch (td->td_state) {
case TDS_RUNNING:
case TDS_RUNQ:
return;
case TDS_INHIBITED:
/*
* If we are only inhibited because we are swapped out
* then arange to swap in this process. Otherwise just return.
*/
if (td->td_inhibitors != TDI_SWAPPED)
return;
/* XXX: intentional fall-through ? */
case TDS_CAN_RUN:
break;
default:
printf("state is 0x%x", td->td_state);
panic("setrunnable(2)");
}
if ((p->p_sflag & PS_INMEM) == 0) {
if ((p->p_sflag & PS_SWAPPINGIN) == 0) {
p->p_sflag |= PS_SWAPINREQ;
wakeup(&proc0);
}
} else
sched_wakeup(td);
}
/*
* Compute a tenex style load average of a quantity on
* 1, 5 and 15 minute intervals.
* XXXKSE Needs complete rewrite when correct info is available.
* Completely Bogus.. only works with 1:1 (but compiles ok now :-)
*/
static void
loadav(void *arg)
{
int i, nrun;
struct loadavg *avg;
struct proc *p;
struct thread *td;
avg = &averunnable;
sx_slock(&allproc_lock);
nrun = 0;
FOREACH_PROC_IN_SYSTEM(p) {
FOREACH_THREAD_IN_PROC(p, td) {
switch (td->td_state) {
case TDS_RUNQ:
case TDS_RUNNING:
if ((p->p_flag & P_NOLOAD) != 0)
goto nextproc;
nrun++; /* XXXKSE */
default:
break;
}
nextproc:
continue;
}
}
sx_sunlock(&allproc_lock);
for (i = 0; i < 3; i++)
avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
/*
* Schedule the next update to occur after 5 seconds, but add a
* random variation to avoid synchronisation with processes that
* run at regular intervals.
*/
callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
loadav, NULL);
}
static void
lboltcb(void *arg)
{
wakeup(&lbolt);
callout_reset(&lbolt_callout, hz, lboltcb, NULL);
}
/* ARGSUSED */
static void
sched_setup(dummy)
void *dummy;
{
callout_init(&loadav_callout, 0);
callout_init(&lbolt_callout, CALLOUT_MPSAFE);
/* Kick off timeout driven events by calling first time. */
loadav(NULL);
lboltcb(NULL);
}
/*
* General purpose yield system call
*/
int
yield(struct thread *td, struct yield_args *uap)
{
struct ksegrp *kg;
kg = td->td_ksegrp;
mtx_assert(&Giant, MA_NOTOWNED);
mtx_lock_spin(&sched_lock);
kg->kg_proc->p_stats->p_ru.ru_nvcsw++;
sched_prio(td, PRI_MAX_TIMESHARE);
mi_switch();
mtx_unlock_spin(&sched_lock);
td->td_retval[0] = 0;
return (0);
}