File: [local] / prex / sys / kern / sched.c (download)
Revision 1.1, Tue Aug 19 12:46:56 2008 UTC (15 years, 8 months ago) by nbrk
Branch point for: MAIN
Initial revision
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/*-
* Copyright (c) 2005-2008, Kohsuke Ohtani
* 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.
* 3. Neither the name of the author nor the names of any co-contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* 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.
*/
/*
* sched.c - scheduler
*/
/**
* General design:
*
* The Prex scheduler is based on the algorithm known as priority
* based multi level queue. Each thread has its own priority
* assigned between 0 and 255. The lower number means higher
* priority like BSD unix. The scheduler maintains 256 level run
* queues mapped to each priority. The lowest priority (=255) is
* used only for an idle thread.
*
* All threads have two different types of priorities:
*
* Base priority:
* This is a static priority used for priority computation.
* A user mode program can change this value via system call.
*
* Current priority:
* An actual scheduling priority. A kernel may adjust this
* priority dynamically if it's needed.
*
* Each thread has one of the following state.
*
* - TH_RUN Running or ready to run
* - TH_SLEEP Sleep for some event
* - TH_SUSPEND Suspend count is not 0
* - TH_EXIT Terminated
*
* The thread is always preemptive even in the kernel mode.
* There are following 4 reasons to switch thread.
*
* (1) Block
* Thread is blocked for sleep or suspend.
* It is put on the tail of the run queue when it becomes
* runnable again.
*
* (2) Preemption
* If higher priority thread becomes runnable, the current
* thread is put on the _head_ of the run queue.
*
* (3) Quantum expiration
* If the thread consumes its time quantum, it is put on
* the tail of the run queue.
*
* (4) Yield
* If the thread releases CPU by itself, it is put on the
* tail of the run queue.
*
* There are following three types of scheduling policies.
*
* - SCHED_FIFO First in-first-out
* - SCHED_RR Round robin (SCHED_FIFO + timeslice)
* - SCHED_OTHER Another scheduling (not supported)
*/
#include <kernel.h>
#include <queue.h>
#include <event.h>
#include <irq.h>
#include <thread.h>
#include <timer.h>
#include <vm.h>
#include <task.h>
#include <system.h>
#include <sched.h>
static struct queue runq[NPRIO]; /* run queues */
static struct queue wakeq; /* queue for waking threads */
static struct queue dpcq; /* DPC queue */
static int top_prio; /* highest priority in runq */
static struct event dpc_event; /* event for DPC */
/*
* Search for highest-priority runnable thread.
*/
static int
runq_top(void)
{
int prio;
for (prio = 0; prio < MIN_PRIO; prio++)
if (!queue_empty(&runq[prio]))
break;
return prio;
}
/*
* Put a thread on the tail of the run queue.
*/
static void
runq_enqueue(thread_t th)
{
enqueue(&runq[th->prio], &th->link);
if (th->prio < top_prio) {
top_prio = th->prio;
cur_thread->resched = 1;
}
}
/*
* Insert a thread to the head of the run queue.
* We assume this routine is called while thread switching.
*/
static void
runq_insert(thread_t th)
{
queue_insert(&runq[th->prio], &th->link);
if (th->prio < top_prio)
top_prio = th->prio;
}
/*
* Pick up and remove the highest-priority thread
* from the run queue.
*/
static thread_t
runq_dequeue(void)
{
queue_t q;
thread_t th;
q = dequeue(&runq[top_prio]);
th = queue_entry(q, struct thread, link);
if (queue_empty(&runq[top_prio]))
top_prio = runq_top();
return th;
}
/*
* Remove the specified thread from the run queue.
*/
static void
runq_remove(thread_t th)
{
queue_remove(&th->link);
top_prio = runq_top();
}
/*
* Process all pending woken threads.
*/
static void
wakeq_flush(void)
{
queue_t q;
thread_t th;
while (!queue_empty(&wakeq)) {
/*
* Set a thread runnable.
*/
q = dequeue(&wakeq);
th = queue_entry(q, struct thread, link);
th->slpevt = NULL;
th->state &= ~TH_SLEEP;
if (th != cur_thread && th->state == TH_RUN)
runq_enqueue(th);
}
}
/*
* sched_switch - this is the scheduler proper:
*
* If the scheduling reason is preemption, the current
* thread will remain at the head of the run queue. So,
* the thread still has right to run first again among
* the same priority threads. For other scheduling reason,
* the current thread is inserted into the tail of the run
* queue.
*/
static void
sched_switch(void)
{
thread_t prev, next;
/*
* Move a current thread to the run queue.
*/
prev = cur_thread;
if (prev->state == TH_RUN) {
if (prev->prio > top_prio)
runq_insert(prev); /* preemption */
else
runq_enqueue(prev);
}
prev->resched = 0;
/*
* Select the thread to run the CPU next.
*/
next = runq_dequeue();
if (next == prev)
return;
cur_thread = next;
/*
* Switch to the new thread.
* You are expected to understand this..
*/
if (prev->task != next->task)
vm_switch(next->task->map);
context_switch(&prev->ctx, &next->ctx);
}
/*
* sleep_expire - sleep timer is expired:
*
* Wake up the thread which is sleeping in sched_tsleep().
*/
static void
sleep_expire(void *arg)
{
sched_unsleep((thread_t)arg, SLP_TIMEOUT);
}
/*
* sched_tsleep - sleep the current thread until a wakeup
* is performed on the specified event.
*
* This routine returns a sleep result. If the thread is
* woken by sched_wakeup() or sched_wakeone(), it returns 0.
* Otherwise, it will return the result value which is passed
* by sched_unsleep(). We allow calling sched_sleep() with
* interrupt disabled.
*
* sched_sleep() is also defined as a wrapper macro for
* sched_tsleep() without timeout. Note that all sleep
* requests are interruptible with this kernel.
*/
int
sched_tsleep(struct event *evt, u_long msec)
{
ASSERT(irq_level == 0);
ASSERT(evt);
sched_lock();
irq_lock();
cur_thread->slpevt = evt;
cur_thread->state |= TH_SLEEP;
enqueue(&evt->sleepq, &cur_thread->link);
if (msec != 0) {
/*
* Program timer to wake us up at timeout.
*/
timer_callout(&cur_thread->timeout, msec, &sleep_expire,
cur_thread);
}
wakeq_flush();
sched_switch(); /* Sleep here. Zzzz.. */
irq_unlock();
sched_unlock();
return cur_thread->slpret;
}
/*
* sched_wakeup - wake up all threads sleeping on event.
*
* A thread can have sleep and suspend state simultaneously.
* So, the thread does not always run even if it woke up.
*
* Since this routine can be called from ISR at interrupt
* level, there may be contention for access to some data.
* Thus, this routine will temporary move the waking thread
* into wakeq, and they will be moved to runq at more safer
* time in wakeq_flush().
*
* The woken thread will be put on the tail of runq
* regardless of its scheduling policy. If woken threads have
* same priority, next running thread is selected by FIFO order.
*/
void
sched_wakeup(struct event *evt)
{
queue_t q;
thread_t th;
ASSERT(evt);
sched_lock();
irq_lock();
while (!queue_empty(&evt->sleepq)) {
/*
* Move a sleeping thread to the wake queue.
*/
q = dequeue(&evt->sleepq);
th = queue_entry(q, struct thread, link);
th->slpret = 0;
enqueue(&wakeq, q);
timer_stop(&th->timeout);
}
irq_unlock();
sched_unlock();
}
/*
* sched_wakeone - wake up one thread sleeping on event.
*
* The highest priority thread is woken among sleeping
* threads. This routine returns the thread ID of the
* woken thread, or NULL if no threads are sleeping.
*/
thread_t
sched_wakeone(struct event *evt)
{
queue_t head, q;
thread_t top, th = NULL;
sched_lock();
irq_lock();
head = &evt->sleepq;
if (!queue_empty(head)) {
/*
* Select the highet priority thread in
* the sleep queue, and wakeup it.
*/
q = queue_first(head);
top = queue_entry(q, struct thread, link);
while (!queue_end(head, q)) {
th = queue_entry(q, struct thread, link);
if (th->prio < top->prio)
top = th;
q = queue_next(q);
}
queue_remove(&top->link);
top->slpret = 0;
enqueue(&wakeq, &top->link);
timer_stop(&top->timeout);
th = top;
}
irq_unlock();
sched_unlock();
return th;
}
/*
* sched_unsleep - cancel sleep.
*
* sched_unsleep() removes the specified thread from its
* sleep queue. The specified sleep result will be passed
* to the sleeping thread as a return value of sched_tsleep().
*/
void
sched_unsleep(thread_t th, int result)
{
sched_lock();
if (th->state & TH_SLEEP) {
irq_lock();
queue_remove(&th->link);
th->slpret = result;
enqueue(&wakeq, &th->link);
timer_stop(&th->timeout);
irq_unlock();
}
sched_unlock();
}
/*
* Yield the current processor to another thread.
*
* Note that the current thread may run immediately again,
* if no other thread exists in the same priority queue.
*/
void
sched_yield(void)
{
sched_lock();
if (!queue_empty(&runq[cur_thread->prio]))
cur_thread->resched = 1;
sched_unlock(); /* Switch current thread here */
}
/*
* Suspend the specified thread.
* Called with scheduler locked.
*/
void
sched_suspend(thread_t th)
{
if (th->state == TH_RUN) {
if (th == cur_thread)
cur_thread->resched = 1;
else
runq_remove(th);
}
th->state |= TH_SUSPEND;
}
/*
* Resume the specified thread.
* Called with scheduler locked.
*/
void
sched_resume(thread_t th)
{
if (th->state & TH_SUSPEND) {
th->state &= ~TH_SUSPEND;
if (th->state == TH_RUN)
runq_enqueue(th);
}
}
/*
* sched_tick() is called from timer_tick() once every tick.
* Check quantum expiration, and mark a rescheduling flag.
* We don't need locking in here.
*/
void
sched_tick(void)
{
/* Profile running time. */
cur_thread->time++;
if (cur_thread->policy == SCHED_RR) {
if (--cur_thread->timeleft <= 0) {
/*
* The quantum is up.
* Give the thread another.
*/
cur_thread->timeleft += QUANTUM;
cur_thread->resched = 1;
}
}
}
/*
* Set up stuff for thread scheduling.
*/
void
sched_start(thread_t th)
{
th->state = TH_RUN | TH_SUSPEND;
th->policy = SCHED_RR;
th->prio = PRIO_USER;
th->baseprio = PRIO_USER;
th->timeleft = QUANTUM;
}
/*
* Stop thread scheduling.
*/
void
sched_stop(thread_t th)
{
if (th == cur_thread) {
/*
* If specified thread is current thread,
* the scheduling lock count is force set
* to 1 to ensure the thread switching in
* the next sched_unlock().
*/
cur_thread->locks = 1;
cur_thread->resched = 1;
} else {
if (th->state == TH_RUN)
runq_remove(th);
else if (th->state & TH_SLEEP)
queue_remove(&th->link);
}
timer_stop(&th->timeout);
th->state = TH_EXIT;
}
/*
* sched_lock - lock the scheduler.
*
* The thread switch is disabled during scheduler locked.
* This is mainly used to synchronize the thread execution
* to protect global resources. Even when scheduler is
* locked, an interrupt handler can run. So, we have to
* use irq_lock() to synchronize a global data with ISR.
*
* Since the scheduling lock can be nested any number of
* times, the caller has the responsible to unlock the same
* number of locks.
*/
void
sched_lock(void)
{
cur_thread->locks++;
}
/*
* sched_unlock - unlock scheduler.
*
* If nobody locks the scheduler anymore, it checks the
* rescheduling flag and kick scheduler if it's marked.
*
* Note that this routine will be always called at the end
* of each interrupt handler.
*/
void
sched_unlock(void)
{
int s;
ASSERT(cur_thread->locks > 0);
interrupt_save(&s);
interrupt_disable();
if (cur_thread->locks == 1) {
wakeq_flush();
while (cur_thread->resched) {
/* Kick scheduler */
sched_switch();
/*
* Now we run pending interrupts which fired
* during the thread switch. So, we can catch
* the rescheduling request from such ISRs.
* Otherwise, the reschedule may be deferred
* until _next_ sched_unlock() call.
*/
interrupt_restore(s);
interrupt_disable();
wakeq_flush();
}
}
cur_thread->locks--;
interrupt_restore(s);
}
int
sched_getprio(thread_t th)
{
return th->prio;
}
/*
* sched_setprio - set priority of thread.
*
* The rescheduling flag is set if the priority is
* better than the currently running thread.
* Called with scheduler locked.
*/
void
sched_setprio(thread_t th, int baseprio, int prio)
{
th->baseprio = baseprio;
if (th == cur_thread) {
/*
* If we change the current thread's priority,
* rescheduling may be happened.
*/
th->prio = prio;
top_prio = runq_top();
if (prio != top_prio)
cur_thread->resched = 1;
} else {
if (th->state == TH_RUN) {
/*
* Update the thread priority and adjust
* the run queue position for new priority.
*/
runq_remove(th);
th->prio = prio;
runq_enqueue(th);
} else
th->prio = prio;
}
}
int
sched_getpolicy(thread_t th)
{
return th->policy;
}
int
sched_setpolicy(thread_t th, int policy)
{
int err = 0;
switch (policy) {
case SCHED_RR:
case SCHED_FIFO:
th->timeleft = QUANTUM;
th->policy = policy;
break;
default:
err = -1;
break;
}
return err;
}
/*
* Schedule DPC callback.
*
* DPC (Deferred Procedure Call) is used to call the specific
* function at some later time with a DPC priority. It is also
* known as AST or SoftIRQ in other kernels. DPC is typically
* used by device drivers to do the low-priority jobs without
* degrading real-time performance.
* This routine can be called from ISR.
*/
void
sched_dpc(struct dpc *dpc, void (*func)(void *), void *arg)
{
ASSERT(dpc);
ASSERT(func);
irq_lock();
/*
* Insert request to DPC queue.
*/
dpc->func = func;
dpc->arg = arg;
if (dpc->state != DPC_PENDING)
enqueue(&dpcq, &dpc->link);
dpc->state = DPC_PENDING;
/* Wake DPC thread */
sched_wakeup(&dpc_event);
irq_unlock();
}
/*
* DPC thread.
*
* This is a kernel thread to process the pending call back
* request within DPC queue. Each DPC routine is called with
* the following conditions.
* - Interrupt is enabled.
* - Scheduler is unlocked.
*/
static void
dpc_thread(void *arg)
{
queue_t q;
struct dpc *dpc;
for (;;) {
/* Wait until next DPC request. */
sched_sleep(&dpc_event);
while (!queue_empty(&dpcq)) {
q = dequeue(&dpcq);
dpc = queue_entry(q, struct dpc, link);
dpc->state = DPC_FREE;
/*
* Call DPC routine.
*/
interrupt_enable();
(*dpc->func)(dpc->arg);
interrupt_disable();
}
}
/* NOTREACHED */
}
/*
* Initialize the global scheduler state.
*/
void
sched_init(void)
{
thread_t th;
int i;
for (i = 0; i < NPRIO; i++)
queue_init(&runq[i]);
queue_init(&wakeq);
queue_init(&dpcq);
event_init(&dpc_event, "dpc");
top_prio = PRIO_IDLE;
cur_thread->resched = 1;
/* Create a DPC thread. */
th = kthread_create(dpc_thread, NULL, PRIO_DPC);
if (th == NULL)
panic("sched_init");
DPRINTF(("Time slice is %d msec\n", CONFIG_TIME_SLICE));
}
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