freebsd-dev/sys/kern/kern_switch.c
2007-06-12 19:50:31 +00:00

634 lines
17 KiB
C

/*-
* Copyright (c) 2001 Jake Burkholder <jake@FreeBSD.org>
* All rights reserved.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_sched.h"
#ifndef KERN_SWITCH_INCLUDE
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/sched.h>
#else /* KERN_SWITCH_INCLUDE */
#if defined(SMP) && (defined(__i386__) || defined(__amd64__))
#include <sys/smp.h>
#endif
#if defined(SMP) && defined(SCHED_4BSD)
#include <sys/sysctl.h>
#endif
#include <machine/cpu.h>
/* Uncomment this to enable logging of critical_enter/exit. */
#if 0
#define KTR_CRITICAL KTR_SCHED
#else
#define KTR_CRITICAL 0
#endif
#ifdef FULL_PREEMPTION
#ifndef PREEMPTION
#error "The FULL_PREEMPTION option requires the PREEMPTION option"
#endif
#endif
CTASSERT((RQB_BPW * RQB_LEN) == RQ_NQS);
/*
* kern.sched.preemption allows user space to determine if preemption support
* is compiled in or not. It is not currently a boot or runtime flag that
* can be changed.
*/
#ifdef PREEMPTION
static int kern_sched_preemption = 1;
#else
static int kern_sched_preemption = 0;
#endif
SYSCTL_INT(_kern_sched, OID_AUTO, preemption, CTLFLAG_RD,
&kern_sched_preemption, 0, "Kernel preemption enabled");
#ifdef SCHED_STATS
long switch_preempt;
long switch_owepreempt;
long switch_turnstile;
long switch_sleepq;
long switch_sleepqtimo;
long switch_relinquish;
long switch_needresched;
static SYSCTL_NODE(_kern_sched, OID_AUTO, stats, CTLFLAG_RW, 0, "switch stats");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, preempt, CTLFLAG_RD, &switch_preempt, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, owepreempt, CTLFLAG_RD, &switch_owepreempt, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, turnstile, CTLFLAG_RD, &switch_turnstile, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, sleepq, CTLFLAG_RD, &switch_sleepq, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, sleepqtimo, CTLFLAG_RD, &switch_sleepqtimo, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, relinquish, CTLFLAG_RD, &switch_relinquish, 0, "");
SYSCTL_INT(_kern_sched_stats, OID_AUTO, needresched, CTLFLAG_RD, &switch_needresched, 0, "");
static int
sysctl_stats_reset(SYSCTL_HANDLER_ARGS)
{
int error;
int val;
val = 0;
error = sysctl_handle_int(oidp, &val, 0, req);
if (error != 0 || req->newptr == NULL)
return (error);
if (val == 0)
return (0);
switch_preempt = 0;
switch_owepreempt = 0;
switch_turnstile = 0;
switch_sleepq = 0;
switch_sleepqtimo = 0;
switch_relinquish = 0;
switch_needresched = 0;
return (0);
}
SYSCTL_PROC(_kern_sched_stats, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_WR, NULL,
0, sysctl_stats_reset, "I", "Reset scheduler statistics");
#endif
/************************************************************************
* Functions that manipulate runnability from a thread perspective. *
************************************************************************/
/*
* Select the thread that will be run next.
*/
struct thread *
choosethread(void)
{
struct thread *td;
#if defined(SMP) && (defined(__i386__) || defined(__amd64__))
if (smp_active == 0 && PCPU_GET(cpuid) != 0) {
/* Shutting down, run idlethread on AP's */
td = PCPU_GET(idlethread);
CTR1(KTR_RUNQ, "choosethread: td=%p (idle)", td);
TD_SET_RUNNING(td);
return (td);
}
#endif
retry:
td = sched_choose();
/*
* If we are in panic, only allow system threads,
* plus the one we are running in, to be run.
*/
if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 &&
(td->td_flags & TDF_INPANIC) == 0)) {
/* note that it is no longer on the run queue */
TD_SET_CAN_RUN(td);
goto retry;
}
TD_SET_RUNNING(td);
return (td);
}
/*
* Kernel thread preemption implementation. Critical sections mark
* regions of code in which preemptions are not allowed.
*/
void
critical_enter(void)
{
struct thread *td;
td = curthread;
td->td_critnest++;
CTR4(KTR_CRITICAL, "critical_enter by thread %p (%ld, %s) to %d", td,
(long)td->td_proc->p_pid, td->td_proc->p_comm, td->td_critnest);
}
void
critical_exit(void)
{
struct thread *td;
td = curthread;
KASSERT(td->td_critnest != 0,
("critical_exit: td_critnest == 0"));
#ifdef PREEMPTION
if (td->td_critnest == 1) {
td->td_critnest = 0;
if (td->td_owepreempt) {
td->td_critnest = 1;
thread_lock(td);
td->td_critnest--;
SCHED_STAT_INC(switch_owepreempt);
mi_switch(SW_INVOL, NULL);
thread_unlock(td);
}
} else
#endif
td->td_critnest--;
CTR4(KTR_CRITICAL, "critical_exit by thread %p (%ld, %s) to %d", td,
(long)td->td_proc->p_pid, td->td_proc->p_comm, td->td_critnest);
}
/*
* This function is called when a thread is about to be put on run queue
* because it has been made runnable or its priority has been adjusted. It
* determines if the new thread should be immediately preempted to. If so,
* it switches to it and eventually returns true. If not, it returns false
* so that the caller may place the thread on an appropriate run queue.
*/
int
maybe_preempt(struct thread *td)
{
#ifdef PREEMPTION
struct thread *ctd;
int cpri, pri;
#endif
#ifdef PREEMPTION
/*
* The new thread should not preempt the current thread if any of the
* following conditions are true:
*
* - The kernel is in the throes of crashing (panicstr).
* - The current thread has a higher (numerically lower) or
* equivalent priority. Note that this prevents curthread from
* trying to preempt to itself.
* - It is too early in the boot for context switches (cold is set).
* - The current thread has an inhibitor set or is in the process of
* exiting. In this case, the current thread is about to switch
* out anyways, so there's no point in preempting. If we did,
* the current thread would not be properly resumed as well, so
* just avoid that whole landmine.
* - If the new thread's priority is not a realtime priority and
* the current thread's priority is not an idle priority and
* FULL_PREEMPTION is disabled.
*
* If all of these conditions are false, but the current thread is in
* a nested critical section, then we have to defer the preemption
* until we exit the critical section. Otherwise, switch immediately
* to the new thread.
*/
ctd = curthread;
THREAD_LOCK_ASSERT(td, MA_OWNED);
KASSERT ((ctd->td_sched != NULL && ctd->td_sched->ts_thread == ctd),
("thread has no (or wrong) sched-private part."));
KASSERT((td->td_inhibitors == 0),
("maybe_preempt: trying to run inhibited thread"));
pri = td->td_priority;
cpri = ctd->td_priority;
if (panicstr != NULL || pri >= cpri || cold /* || dumping */ ||
TD_IS_INHIBITED(ctd))
return (0);
#ifndef FULL_PREEMPTION
if (pri > PRI_MAX_ITHD && cpri < PRI_MIN_IDLE)
return (0);
#endif
if (ctd->td_critnest > 1) {
CTR1(KTR_PROC, "maybe_preempt: in critical section %d",
ctd->td_critnest);
ctd->td_owepreempt = 1;
return (0);
}
/*
* Thread is runnable but not yet put on system run queue.
*/
MPASS(ctd->td_lock == &sched_lock);
MPASS(td->td_lock == &sched_lock);
MPASS(TD_ON_RUNQ(td));
TD_SET_RUNNING(td);
CTR3(KTR_PROC, "preempting to thread %p (pid %d, %s)\n", td,
td->td_proc->p_pid, td->td_proc->p_comm);
SCHED_STAT_INC(switch_preempt);
mi_switch(SW_INVOL|SW_PREEMPT, td);
/*
* td's lock pointer may have changed. We have to return with it
* locked.
*/
spinlock_enter();
thread_unlock(ctd);
thread_lock(td);
spinlock_exit();
return (1);
#else
return (0);
#endif
}
#if 0
#ifndef PREEMPTION
/* XXX: There should be a non-static version of this. */
static void
printf_caddr_t(void *data)
{
printf("%s", (char *)data);
}
static char preempt_warning[] =
"WARNING: Kernel preemption is disabled, expect reduced performance.\n";
SYSINIT(preempt_warning, SI_SUB_COPYRIGHT, SI_ORDER_ANY, printf_caddr_t,
preempt_warning)
#endif
#endif
/************************************************************************
* SYSTEM RUN QUEUE manipulations and tests *
************************************************************************/
/*
* Initialize a run structure.
*/
void
runq_init(struct runq *rq)
{
int i;
bzero(rq, sizeof *rq);
for (i = 0; i < RQ_NQS; i++)
TAILQ_INIT(&rq->rq_queues[i]);
}
/*
* Clear the status bit of the queue corresponding to priority level pri,
* indicating that it is empty.
*/
static __inline void
runq_clrbit(struct runq *rq, int pri)
{
struct rqbits *rqb;
rqb = &rq->rq_status;
CTR4(KTR_RUNQ, "runq_clrbit: bits=%#x %#x bit=%#x word=%d",
rqb->rqb_bits[RQB_WORD(pri)],
rqb->rqb_bits[RQB_WORD(pri)] & ~RQB_BIT(pri),
RQB_BIT(pri), RQB_WORD(pri));
rqb->rqb_bits[RQB_WORD(pri)] &= ~RQB_BIT(pri);
}
/*
* Find the index of the first non-empty run queue. This is done by
* scanning the status bits, a set bit indicates a non-empty queue.
*/
static __inline int
runq_findbit(struct runq *rq)
{
struct rqbits *rqb;
int pri;
int i;
rqb = &rq->rq_status;
for (i = 0; i < RQB_LEN; i++)
if (rqb->rqb_bits[i]) {
pri = RQB_FFS(rqb->rqb_bits[i]) + (i << RQB_L2BPW);
CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d",
rqb->rqb_bits[i], i, pri);
return (pri);
}
return (-1);
}
static __inline int
runq_findbit_from(struct runq *rq, u_char start)
{
struct rqbits *rqb;
int bit;
int pri;
int i;
rqb = &rq->rq_status;
bit = start & (RQB_BPW -1);
pri = 0;
CTR1(KTR_RUNQ, "runq_findbit_from: start %d", start);
again:
for (i = RQB_WORD(start); i < RQB_LEN; i++) {
CTR3(KTR_RUNQ, "runq_findbit_from: bits %d = %#x bit = %d",
i, rqb->rqb_bits[i], bit);
if (rqb->rqb_bits[i]) {
if (bit != 0) {
for (pri = bit; pri < RQB_BPW; pri++)
if (rqb->rqb_bits[i] & (1ul << pri))
break;
bit = 0;
if (pri >= RQB_BPW)
continue;
} else
pri = RQB_FFS(rqb->rqb_bits[i]);
pri += (i << RQB_L2BPW);
CTR3(KTR_RUNQ, "runq_findbit_from: bits=%#x i=%d pri=%d",
rqb->rqb_bits[i], i, pri);
return (pri);
}
bit = 0;
}
if (start != 0) {
CTR0(KTR_RUNQ, "runq_findbit_from: restarting");
start = 0;
goto again;
}
return (-1);
}
/*
* Set the status bit of the queue corresponding to priority level pri,
* indicating that it is non-empty.
*/
static __inline void
runq_setbit(struct runq *rq, int pri)
{
struct rqbits *rqb;
rqb = &rq->rq_status;
CTR4(KTR_RUNQ, "runq_setbit: bits=%#x %#x bit=%#x word=%d",
rqb->rqb_bits[RQB_WORD(pri)],
rqb->rqb_bits[RQB_WORD(pri)] | RQB_BIT(pri),
RQB_BIT(pri), RQB_WORD(pri));
rqb->rqb_bits[RQB_WORD(pri)] |= RQB_BIT(pri);
}
/*
* Add the thread to the queue specified by its priority, and set the
* corresponding status bit.
*/
void
runq_add(struct runq *rq, struct td_sched *ts, int flags)
{
struct rqhead *rqh;
int pri;
pri = ts->ts_thread->td_priority / RQ_PPQ;
ts->ts_rqindex = pri;
runq_setbit(rq, pri);
rqh = &rq->rq_queues[pri];
CTR5(KTR_RUNQ, "runq_add: td=%p ts=%p pri=%d %d rqh=%p",
ts->ts_thread, ts, ts->ts_thread->td_priority, pri, rqh);
if (flags & SRQ_PREEMPTED) {
TAILQ_INSERT_HEAD(rqh, ts, ts_procq);
} else {
TAILQ_INSERT_TAIL(rqh, ts, ts_procq);
}
}
void
runq_add_pri(struct runq *rq, struct td_sched *ts, u_char pri, int flags)
{
struct rqhead *rqh;
KASSERT(pri < RQ_NQS, ("runq_add_pri: %d out of range", pri));
ts->ts_rqindex = pri;
runq_setbit(rq, pri);
rqh = &rq->rq_queues[pri];
CTR5(KTR_RUNQ, "runq_add_pri: td=%p ke=%p pri=%d idx=%d rqh=%p",
ts->ts_thread, ts, ts->ts_thread->td_priority, pri, rqh);
if (flags & SRQ_PREEMPTED) {
TAILQ_INSERT_HEAD(rqh, ts, ts_procq);
} else {
TAILQ_INSERT_TAIL(rqh, ts, ts_procq);
}
}
/*
* Return true if there are runnable processes of any priority on the run
* queue, false otherwise. Has no side effects, does not modify the run
* queue structure.
*/
int
runq_check(struct runq *rq)
{
struct rqbits *rqb;
int i;
rqb = &rq->rq_status;
for (i = 0; i < RQB_LEN; i++)
if (rqb->rqb_bits[i]) {
CTR2(KTR_RUNQ, "runq_check: bits=%#x i=%d",
rqb->rqb_bits[i], i);
return (1);
}
CTR0(KTR_RUNQ, "runq_check: empty");
return (0);
}
#if defined(SMP) && defined(SCHED_4BSD)
int runq_fuzz = 1;
SYSCTL_INT(_kern_sched, OID_AUTO, runq_fuzz, CTLFLAG_RW, &runq_fuzz, 0, "");
#endif
/*
* Find the highest priority process on the run queue.
*/
struct td_sched *
runq_choose(struct runq *rq)
{
struct rqhead *rqh;
struct td_sched *ts;
int pri;
while ((pri = runq_findbit(rq)) != -1) {
rqh = &rq->rq_queues[pri];
#if defined(SMP) && defined(SCHED_4BSD)
/* fuzz == 1 is normal.. 0 or less are ignored */
if (runq_fuzz > 1) {
/*
* In the first couple of entries, check if
* there is one for our CPU as a preference.
*/
int count = runq_fuzz;
int cpu = PCPU_GET(cpuid);
struct td_sched *ts2;
ts2 = ts = TAILQ_FIRST(rqh);
while (count-- && ts2) {
if (ts->ts_thread->td_lastcpu == cpu) {
ts = ts2;
break;
}
ts2 = TAILQ_NEXT(ts2, ts_procq);
}
} else
#endif
ts = TAILQ_FIRST(rqh);
KASSERT(ts != NULL, ("runq_choose: no proc on busy queue"));
CTR3(KTR_RUNQ,
"runq_choose: pri=%d td_sched=%p rqh=%p", pri, ts, rqh);
return (ts);
}
CTR1(KTR_RUNQ, "runq_choose: idleproc pri=%d", pri);
return (NULL);
}
struct td_sched *
runq_choose_from(struct runq *rq, u_char idx)
{
struct rqhead *rqh;
struct td_sched *ts;
int pri;
if ((pri = runq_findbit_from(rq, idx)) != -1) {
rqh = &rq->rq_queues[pri];
ts = TAILQ_FIRST(rqh);
KASSERT(ts != NULL, ("runq_choose: no proc on busy queue"));
CTR4(KTR_RUNQ,
"runq_choose_from: pri=%d kse=%p idx=%d rqh=%p",
pri, ts, ts->ts_rqindex, rqh);
return (ts);
}
CTR1(KTR_RUNQ, "runq_choose_from: idleproc pri=%d", pri);
return (NULL);
}
/*
* Remove the thread from the queue specified by its priority, and clear the
* corresponding status bit if the queue becomes empty.
* Caller must set state afterwards.
*/
void
runq_remove(struct runq *rq, struct td_sched *ts)
{
runq_remove_idx(rq, ts, NULL);
}
void
runq_remove_idx(struct runq *rq, struct td_sched *ts, u_char *idx)
{
struct rqhead *rqh;
u_char pri;
KASSERT(ts->ts_thread->td_proc->p_sflag & PS_INMEM,
("runq_remove_idx: process swapped out"));
pri = ts->ts_rqindex;
KASSERT(pri < RQ_NQS, ("runq_remove_idx: Invalid index %d\n", pri));
rqh = &rq->rq_queues[pri];
CTR5(KTR_RUNQ, "runq_remove_idx: td=%p, ts=%p pri=%d %d rqh=%p",
ts->ts_thread, ts, ts->ts_thread->td_priority, pri, rqh);
{
struct td_sched *nts;
TAILQ_FOREACH(nts, rqh, ts_procq)
if (nts == ts)
break;
if (ts != nts)
panic("runq_remove_idx: ts %p not on rqindex %d",
ts, pri);
}
TAILQ_REMOVE(rqh, ts, ts_procq);
if (TAILQ_EMPTY(rqh)) {
CTR0(KTR_RUNQ, "runq_remove_idx: empty");
runq_clrbit(rq, pri);
if (idx != NULL && *idx == pri)
*idx = (pri + 1) % RQ_NQS;
}
}
/****** functions that are temporarily here ***********/
#include <vm/uma.h>
extern struct mtx kse_zombie_lock;
/*
* Allocate scheduler specific per-process resources.
* The thread and proc have already been linked in.
*
* Called from:
* proc_init() (UMA init method)
*/
void
sched_newproc(struct proc *p, struct thread *td)
{
}
/*
* thread is being either created or recycled.
* Fix up the per-scheduler resources associated with it.
* Called from:
* sched_fork_thread()
* thread_dtor() (*may go away)
* thread_init() (*may go away)
*/
void
sched_newthread(struct thread *td)
{
struct td_sched *ts;
ts = (struct td_sched *) (td + 1);
bzero(ts, sizeof(*ts));
td->td_sched = ts;
ts->ts_thread = td;
}
#endif /* KERN_SWITCH_INCLUDE */