/*
* Copyright (C) 2001-2004 Jakub Jermar
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - 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.
* - The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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 <proc/scheduler.h>
#include <proc/thread.h>
#include <proc/task.h>
#include <cpu.h>
#include <mm/vm.h>
#include <config.h>
#include <context.h>
#include <func.h>
#include <arch.h>
#include <arch/asm.h>
#include <list.h>
#include <typedefs.h>
#include <mm/page.h>
#include <synch/spinlock.h>
#ifdef __SMP__
#include <arch/smp/atomic.h>
#endif /* __SMP__ */
/*
* NOTE ON ATOMIC READS:
* Some architectures cannot read __u32 atomically.
* For that reason, all accesses to nrdy and the likes must be protected by spinlock.
*/
spinlock_t nrdylock;
volatile int nrdy;
void before_thread_runs(void)
{
before_thread_runs_arch();
fpu_context_restore(&(THREAD->saved_fpu_context));
}
void scheduler_init(void)
{
spinlock_initialize(&nrdylock);
}
/* cpu_priority_high()'d */
struct thread *find_best_thread(void)
{
thread_t *t;
runq_t *r;
int i, n;
loop:
cpu_priority_high();
spinlock_lock(&CPU->lock);
n = CPU->nrdy;
spinlock_unlock(&CPU->lock);
cpu_priority_low();
if (n == 0) {
#ifdef __SMP__
/*
* If the load balancing thread is not running, wake it up and
* set CPU-private flag that the kcpulb has been started.
*/
if (test_and_set(&CPU->kcpulbstarted) == 0) {
waitq_wakeup(&CPU->kcpulb_wq, 0);
goto loop;
}
#endif /* __SMP__ */
/*
* For there was nothing to run, the CPU goes to sleep
* until a hardware interrupt or an IPI comes.
* This improves energy saving and hyperthreading.
* On the other hand, several hardware interrupts can be ignored.
*/
cpu_sleep();
goto loop;
}
cpu_priority_high();
for (i = 0; i<RQ_COUNT; i++) {
r = &CPU->rq[i];
spinlock_lock(&r->lock);
if (r->n == 0) {
/*
* If this queue is empty, try a lower-priority queue.
*/
spinlock_unlock(&r->lock);
continue;
}
spinlock_lock(&nrdylock);
nrdy--;
spinlock_unlock(&nrdylock);
spinlock_lock(&CPU->lock);
CPU->nrdy--;
spinlock_unlock(&CPU->lock);
r->n--;
/*
* Take the first thread from the queue.
*/
t = list_get_instance(r->rq_head.next, thread_t, rq_link);
list_remove(&t->rq_link);
spinlock_unlock(&r->lock);
spinlock_lock(&t->lock);
t->cpu = CPU;
t->ticks = us2ticks((i+1)*10000);
t->pri = i; /* eventually correct rq index */
/*
* Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
*/
t->flags &= ~X_STOLEN;
spinlock_unlock(&t->lock);
return t;
}
goto loop;
}
/*
* This function prevents low priority threads from starving in rq's.
* When it decides to relink rq's, it reconnects respective pointers
* so that in result threads with 'pri' greater or equal 'start' are
* moved to a higher-priority queue.
*/
void relink_rq(int start)
{
link_t head;
runq_t *r;
int i, n;
list_initialize(&head);
spinlock_lock(&CPU->lock);
if (CPU->needs_relink > NEEDS_RELINK_MAX) {
for (i = start; i<RQ_COUNT-1; i++) {
/* remember and empty rq[i + 1] */
r = &CPU->rq[i + 1];
spinlock_lock(&r->lock);
list_concat(&head, &r->rq_head);
n = r->n;
r->n = 0;
spinlock_unlock(&r->lock);
/* append rq[i + 1] to rq[i] */
r = &CPU->rq[i];
spinlock_lock(&r->lock);
list_concat(&r->rq_head, &head);
r->n += n;
spinlock_unlock(&r->lock);
}
CPU->needs_relink = 0;
}
spinlock_unlock(&CPU->lock);
}
/*
* The scheduler.
*/
void scheduler(void)
{
volatile pri_t pri;
pri = cpu_priority_high();
if (haltstate)
halt();
if (THREAD) {
spinlock_lock(&THREAD->lock);
fpu_context_save(&(THREAD->saved_fpu_context));
if (!context_save(&THREAD->saved_context)) {
/*
* This is the place where threads leave scheduler();
*/
before_thread_runs();
spinlock_unlock(&THREAD->lock);
cpu_priority_restore(THREAD->saved_context.pri);
return;
}
THREAD->saved_context.pri = pri;
}
/*
* We may not keep the old stack.
* Reason: If we kept the old stack and got blocked, for instance, in
* find_best_thread(), the old thread could get rescheduled by another
* CPU and overwrite the part of its own stack that was also used by
* the scheduler on this CPU.
*
* Moreover, we have to bypass the compiler-generated POP sequence
* which is fooled by SP being set to the very top of the stack.
* Therefore the scheduler() function continues in
* scheduler_separated_stack().
*/
context_save(&CPU->saved_context);
CPU->saved_context.sp = (__address) &CPU->stack[CPU_STACK_SIZE-8];
CPU->saved_context.pc = (__address) scheduler_separated_stack;
context_restore(&CPU->saved_context);
/* not reached */
}
void scheduler_separated_stack(void)
{
int priority;
if (THREAD) {
switch (THREAD->state) {
case Running:
THREAD->state = Ready;
spinlock_unlock(&THREAD->lock);
thread_ready(THREAD);
break;
case Exiting:
frame_free((__address) THREAD->kstack);
if (THREAD->ustack) {
frame_free((__address) THREAD->ustack);
}
/*
* Detach from the containing task.
*/
spinlock_lock(&TASK->lock);
list_remove(&THREAD->th_link);
spinlock_unlock(&TASK->lock);
spinlock_unlock(&THREAD->lock);
spinlock_lock(&threads_lock);
list_remove(&THREAD->threads_link);
spinlock_unlock(&threads_lock);
break;
case Sleeping:
/*
* Prefer the thread after it's woken up.
*/
THREAD->pri = -1;
/*
* We need to release wq->lock which we locked in waitq_sleep().
* Address of wq->lock is kept in THREAD->sleep_queue.
*/
spinlock_unlock(&THREAD->sleep_queue->lock);
/*
* Check for possible requests for out-of-context invocation.
*/
if (THREAD->call_me) {
THREAD->call_me(THREAD->call_me_with);
THREAD->call_me = NULL;
THREAD->call_me_with = NULL;
}
spinlock_unlock(&THREAD->lock);
break;
default:
/*
* Entering state is unexpected.
*/
panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
break;
}
THREAD = NULL;
}
THREAD = find_best_thread();
spinlock_lock(&THREAD->lock);
priority = THREAD->pri;
spinlock_unlock(&THREAD->lock);
relink_rq(priority);
spinlock_lock(&THREAD->lock);
/*
* If both the old and the new task are the same, lots of work is avoided.
*/
if (TASK != THREAD->task) {
vm_t *m1 = NULL;
vm_t *m2;
if (TASK) {
spinlock_lock(&TASK->lock);
m1 = TASK->vm;
spinlock_unlock(&TASK->lock);
}
spinlock_lock(&THREAD->task->lock);
m2 = THREAD->task->vm;
spinlock_unlock(&THREAD->task->lock);
/*
* Note that it is possible for two tasks to share one vm mapping.
*/
if (m1 != m2) {
/*
* Both tasks and vm mappings are different.
* Replace the old one with the new one.
*/
if (m1) {
vm_uninstall(m1);
}
vm_install(m2);
}
TASK = THREAD->task;
}
THREAD->state = Running;
#ifdef SCHEDULER_VERBOSE
printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU
->id
, THREAD
->tid
, THREAD
->pri
, THREAD
->ticks
, CPU
->nrdy
); #endif
context_restore(&THREAD->saved_context);
/* not reached */
}
#ifdef __SMP__
/*
* This is the load balancing thread.
* It supervises thread supplies for the CPU it's wired to.
*/
void kcpulb(void *arg)
{
thread_t *t;
int count, i, j, k = 0;
pri_t pri;
loop:
/*
* Sleep until there's some work to do.
*/
waitq_sleep(&CPU->kcpulb_wq);
not_satisfied:
/*
* Calculate the number of threads that will be migrated/stolen from
* other CPU's. Note that situation can have changed between two
* passes. Each time get the most up to date counts.
*/
pri = cpu_priority_high();
spinlock_lock(&CPU->lock);
count = nrdy / config.cpu_active;
count -= CPU->nrdy;
spinlock_unlock(&CPU->lock);
cpu_priority_restore(pri);
if (count <= 0)
goto satisfied;
/*
* Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
*/
for (j=RQ_COUNT-1; j >= 0; j--) {
for (i=0; i < config.cpu_active; i++) {
link_t *l;
runq_t *r;
cpu_t *cpu;
cpu = &cpus[(i + k) % config.cpu_active];
r = &cpu->rq[j];
/*
* Not interested in ourselves.
* Doesn't require interrupt disabling for kcpulb is X_WIRED.
*/
if (CPU == cpu)
continue;
restart: pri = cpu_priority_high();
spinlock_lock(&r->lock);
if (r->n == 0) {
spinlock_unlock(&r->lock);
cpu_priority_restore(pri);
continue;
}
t = NULL;
l = r->rq_head.prev; /* search rq from the back */
while (l != &r->rq_head) {
t = list_get_instance(l, thread_t, rq_link);
/*
* We don't want to steal CPU-wired threads neither threads already stolen.
* The latter prevents threads from migrating between CPU's without ever being run.
*/
spinlock_lock(&t->lock);
if (!(t->flags & (X_WIRED | X_STOLEN))) {
/*
* Remove t from r.
*/
spinlock_unlock(&t->lock);
/*
* Here we have to avoid deadlock with relink_rq(),
* because it locks cpu and r in a different order than we do.
*/
if (!spinlock_trylock(&cpu->lock)) {
/* Release all locks and try again. */
spinlock_unlock(&r->lock);
cpu_priority_restore(pri);
goto restart;
}
cpu->nrdy--;
spinlock_unlock(&cpu->lock);
spinlock_lock(&nrdylock);
nrdy--;
spinlock_unlock(&nrdylock);
r->n--;
list_remove(&t->rq_link);
break;
}
spinlock_unlock(&t->lock);
l = l->prev;
t = NULL;
}
spinlock_unlock(&r->lock);
if (t) {
/*
* Ready t on local CPU
*/
spinlock_lock(&t->lock);
#ifdef KCPULB_VERBOSE
printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU
->id
, t
->tid
, CPU
->id
, CPU
->nrdy
, nrdy
/ config.
cpu_active); #endif
t->flags |= X_STOLEN;
spinlock_unlock(&t->lock);
thread_ready(t);
cpu_priority_restore(pri);
if (--count == 0)
goto satisfied;
/*
* We are not satisfied yet, focus on another CPU next time.
*/
k++;
continue;
}
cpu_priority_restore(pri);
}
}
if (CPU->nrdy) {
/*
* Be a little bit light-weight and let migrated threads run.
*/
scheduler();
}
else {
/*
* We failed to migrate a single thread.
* Something more sophisticated should be done.
*/
scheduler();
}
goto not_satisfied;
satisfied:
/*
* Tell find_best_thread() to wake us up later again.
*/
CPU->kcpulbstarted = 0;
goto loop;
}
#endif /* __SMP__ */