freebsd-dev/sys/kern/kern_switch.c

299 lines
7.2 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.
*
* $FreeBSD$
*/
#include <sys/param.h>
#include <sys/systm.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>
/*
* Global run queue.
*/
static struct runq runq;
SYSINIT(runq, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, runq_init, &runq)
/*
* Wrappers which implement old interface; act on global run queue.
*/
struct thread *
choosethread(void)
{
return (runq_choose(&runq)->ke_thread);
}
int
procrunnable(void)
{
return runq_check(&runq);
}
void
remrunqueue(struct thread *td)
{
runq_remove(&runq, td->td_kse);
}
void
setrunqueue(struct thread *td)
{
runq_add(&runq, td->td_kse);
}
/* Critical sections that prevent preemption. */
void
critical_enter(void)
{
struct thread *td;
td = curthread;
if (td->td_critnest == 0)
td->td_savecrit = cpu_critical_enter();
td->td_critnest++;
}
void
critical_exit(void)
{
struct thread *td;
td = curthread;
if (td->td_critnest == 1) {
td->td_critnest = 0;
cpu_critical_exit(td->td_savecrit);
} else
td->td_critnest--;
}
/*
* 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]) - 1) +
(i << RQB_L2BPW);
CTR3(KTR_RUNQ, "runq_findbit: bits=%#x i=%d pri=%d",
rqb->rqb_bits[i], i, pri);
return (pri);
}
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);
}
#ifdef INVARIANT_SUPPORT
/*
* Return true if the specified process is already in the run queue.
*/
static __inline int
runq_find(struct runq *rq, struct kse *ke)
{
struct kse *ke2;
int i;
mtx_assert(&sched_lock, MA_OWNED);
for (i = 0; i < RQB_LEN; i++)
TAILQ_FOREACH(ke2, &rq->rq_queues[i], ke_procq)
if (ke2 == ke)
return 1;
return 0;
}
#endif
/*
* Add the process to the queue specified by its priority, and set the
* corresponding status bit.
*/
void
runq_add(struct runq *rq, struct kse *ke)
{
struct rqhead *rqh;
int pri;
#ifdef INVARIANTS
struct proc *p = ke->ke_proc;
#endif
if (ke->ke_flags & KEF_ONRUNQ)
return;
mtx_assert(&sched_lock, MA_OWNED);
KASSERT(p->p_stat == SRUN, ("runq_add: proc %p (%s) not SRUN",
p, p->p_comm));
KASSERT(runq_find(rq, ke) == 0,
("runq_add: proc %p (%s) already in run queue", ke, p->p_comm));
pri = ke->ke_thread->td_priority / RQ_PPQ;
ke->ke_rqindex = pri;
runq_setbit(rq, pri);
rqh = &rq->rq_queues[pri];
CTR4(KTR_RUNQ, "runq_add: p=%p pri=%d %d rqh=%p",
ke->ke_proc, ke->ke_thread->td_priority, pri, rqh);
TAILQ_INSERT_TAIL(rqh, ke, ke_procq);
ke->ke_flags |= KEF_ONRUNQ;
}
/*
* 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);
}
/*
* Find and remove the highest priority process from the run queue.
* If there are no runnable processes, the per-cpu idle process is
* returned. Will not return NULL under any circumstances.
*/
struct kse *
runq_choose(struct runq *rq)
{
struct rqhead *rqh;
struct kse *ke;
int pri;
mtx_assert(&sched_lock, MA_OWNED);
if ((pri = runq_findbit(rq)) != -1) {
rqh = &rq->rq_queues[pri];
ke = TAILQ_FIRST(rqh);
KASSERT(ke != NULL, ("runq_choose: no proc on busy queue"));
KASSERT(ke->ke_proc->p_stat == SRUN,
("runq_choose: process %d(%s) in state %d", ke->ke_proc->p_pid,
ke->ke_proc->p_comm, ke->ke_proc->p_stat));
CTR3(KTR_RUNQ, "runq_choose: pri=%d kse=%p rqh=%p", pri, ke, rqh);
TAILQ_REMOVE(rqh, ke, ke_procq);
if (TAILQ_EMPTY(rqh)) {
CTR0(KTR_RUNQ, "runq_choose: empty");
runq_clrbit(rq, pri);
}
ke->ke_flags &= ~KEF_ONRUNQ;
return (ke);
}
CTR1(KTR_RUNQ, "runq_choose: idleproc pri=%d", pri);
return (PCPU_GET(idlethread)->td_kse);
}
/*
* 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]);
}
/*
* Remove the process from the queue specified by its priority, and clear the
* corresponding status bit if the queue becomes empty.
*/
void
runq_remove(struct runq *rq, struct kse *ke)
{
struct rqhead *rqh;
int pri;
if (!(ke->ke_flags & KEF_ONRUNQ))
return;
mtx_assert(&sched_lock, MA_OWNED);
pri = ke->ke_rqindex;
rqh = &rq->rq_queues[pri];
CTR4(KTR_RUNQ, "runq_remove: p=%p pri=%d %d rqh=%p",
ke, ke->ke_thread->td_priority, pri, rqh);
KASSERT(ke != NULL, ("runq_remove: no proc on busy queue"));
TAILQ_REMOVE(rqh, ke, ke_procq);
if (TAILQ_EMPTY(rqh)) {
CTR0(KTR_RUNQ, "runq_remove: empty");
runq_clrbit(rq, pri);
}
ke->ke_flags &= ~KEF_ONRUNQ;
}