kernel/sched.c

/*
 * Copyright (c) 2016-2017 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <kernel.h>
#include <kernel_structs.h>
#include <atomic.h>
#include <ksched.h>
#include <wait_q.h>
#include <misc/util.h>

/* the only struct _kernel instance */
struct _kernel _kernel = {0};

/* set the bit corresponding to prio in ready q bitmap */
#ifdef CONFIG_MULTITHREADING
static void _set_ready_q_prio_bit(int prio)
{
	int bmap_index = _get_ready_q_prio_bmap_index(prio);
	u32_t *bmap = &_ready_q.prio_bmap[bmap_index];

	*bmap |= _get_ready_q_prio_bit(prio);
}
#endif

/* clear the bit corresponding to prio in ready q bitmap */
#ifdef CONFIG_MULTITHREADING
static void _clear_ready_q_prio_bit(int prio)
{
	int bmap_index = _get_ready_q_prio_bmap_index(prio);
	u32_t *bmap = &_ready_q.prio_bmap[bmap_index];

	*bmap &= ~_get_ready_q_prio_bit(prio);
}
#endif

#ifdef CONFIG_MULTITHREADING
/*
 * Find the next thread to run when there is no thread in the cache and update
 * the cache.
 */
static struct k_thread *_get_ready_q_head(void)
{
	int prio = _get_highest_ready_prio();
	int q_index = _get_ready_q_q_index(prio);
	sys_dlist_t *list = &_ready_q.q[q_index];

	__ASSERT(!sys_dlist_is_empty(list),
		 "no thread to run (prio: %d, queue index: %u)!\n",
		 prio, q_index);

	struct k_thread *thread =
		(struct k_thread *)sys_dlist_peek_head_not_empty(list);

	return thread;
}
#endif

/*
 * Add thread to the ready queue, in the slot for its priority; the thread
 * must not be on a wait queue.
 *
 * This function, along with _move_thread_to_end_of_prio_q(), are the _only_
 * places where a thread is put on the ready queue.
 *
 * Interrupts must be locked when calling this function.
 */

void _add_thread_to_ready_q(struct k_thread *thread)
{
#ifdef CONFIG_MULTITHREADING
	int q_index = _get_ready_q_q_index(thread->base.prio);
	sys_dlist_t *q = &_ready_q.q[q_index];

	_set_ready_q_prio_bit(thread->base.prio);
	sys_dlist_append(q, &thread->base.k_q_node);

	struct k_thread **cache = &_ready_q.cache;

	*cache = _is_t1_higher_prio_than_t2(thread, *cache) ? thread : *cache;
#else
	sys_dlist_append(&_ready_q.q[0], &thread->base.k_q_node);
	_ready_q.prio_bmap[0] = 1;
	_ready_q.cache = thread;
#endif
}

/*
 * This function, along with _move_thread_to_end_of_prio_q(), are the _only_
 * places where a thread is taken off the ready queue.
 *
 * Interrupts must be locked when calling this function.
 */

void _remove_thread_from_ready_q(struct k_thread *thread)
{
#ifdef CONFIG_MULTITHREADING
	int q_index = _get_ready_q_q_index(thread->base.prio);
	sys_dlist_t *q = &_ready_q.q[q_index];

	sys_dlist_remove(&thread->base.k_q_node);
	if (sys_dlist_is_empty(q)) {
		_clear_ready_q_prio_bit(thread->base.prio);
	}

	struct k_thread **cache = &_ready_q.cache;

	*cache = *cache == thread ? _get_ready_q_head() : *cache;
#else
	_ready_q.prio_bmap[0] = 0;
	_ready_q.cache = NULL;
	sys_dlist_remove(&thread->base.k_q_node);
#endif
}

/* reschedule threads if the scheduler is not locked */
/* not callable from ISR */
/* must be called with interrupts locked */
void _reschedule_threads(int key)
{
#ifdef CONFIG_PREEMPT_ENABLED
	K_DEBUG("rescheduling threads\n");

	if (_must_switch_threads()) {
		K_DEBUG("context-switching out %p\n", _current);
		_Swap(key);
	} else {
		irq_unlock(key);
	}
#else
	irq_unlock(key);
#endif
}

void k_sched_lock(void)
{
#ifdef CONFIG_PREEMPT_ENABLED
	__ASSERT(_current->base.sched_locked != 1, "");
	__ASSERT(!_is_in_isr(), "");

	--_current->base.sched_locked;

	/* Probably not needed since we're in a real function,
	 * but it doesn't hurt.
	 */
	compiler_barrier();

	K_DEBUG("scheduler locked (%p:%d)\n",
		_current, _current->base.sched_locked);
#endif
}

void k_sched_unlock(void)
{
#ifdef CONFIG_PREEMPT_ENABLED
	__ASSERT(_current->base.sched_locked != 0, "");
	__ASSERT(!_is_in_isr(), "");

	int key = irq_lock();

	/* compiler_barrier() not needed, comes from irq_lock() */

	++_current->base.sched_locked;

	K_DEBUG("scheduler unlocked (%p:%d)\n",
		_current, _current->base.sched_locked);

	_reschedule_threads(key);
#endif
}

/* convert milliseconds to ticks */

#ifdef _NON_OPTIMIZED_TICKS_PER_SEC
s32_t _ms_to_ticks(s32_t ms)
{
	s64_t ms_ticks_per_sec = (s64_t)ms * sys_clock_ticks_per_sec;

	return (s32_t)ceiling_fraction(ms_ticks_per_sec, MSEC_PER_SEC);
}
#endif

/* pend the specified thread: it must *not* be in the ready queue */
/* must be called with interrupts locked */
void _pend_thread(struct k_thread *thread, _wait_q_t *wait_q, s32_t timeout)
{
#ifdef CONFIG_MULTITHREADING
	sys_dlist_t *wait_q_list = (sys_dlist_t *)wait_q;
	sys_dnode_t *node;

	SYS_DLIST_FOR_EACH_NODE(wait_q_list, node) {
		struct k_thread *pending = (struct k_thread *)node;

		if (_is_t1_higher_prio_than_t2(thread, pending)) {
			sys_dlist_insert_before(wait_q_list, node,
						&thread->base.k_q_node);
			goto inserted;
		}
	}

	sys_dlist_append(wait_q_list, &thread->base.k_q_node);

inserted:
	_mark_thread_as_pending(thread);

	if (timeout != K_FOREVER) {
		s32_t ticks = _TICK_ALIGN + _ms_to_ticks(timeout);

		_add_thread_timeout(thread, wait_q, ticks);
	}
#endif
}

/* pend the current thread */
/* must be called with interrupts locked */
void _pend_current_thread(_wait_q_t *wait_q, s32_t timeout)
{
	_remove_thread_from_ready_q(_current);
	_pend_thread(_current, wait_q, timeout);
}

#if defined(CONFIG_PREEMPT_ENABLED) && defined(CONFIG_KERNEL_DEBUG)
/* debug aid */
static void _dump_ready_q(void)
{
	K_DEBUG("bitmaps: ");
	for (int bitmap = 0; bitmap < K_NUM_PRIO_BITMAPS; bitmap++) {
		K_DEBUG("%x", _ready_q.prio_bmap[bitmap]);
	}
	K_DEBUG("\n");
	for (int prio = 0; prio < K_NUM_PRIORITIES; prio++) {
		K_DEBUG("prio: %d, head: %p\n",
			prio - _NUM_COOP_PRIO,
			sys_dlist_peek_head(&_ready_q.q[prio]));
	}
}
#endif  /* CONFIG_PREEMPT_ENABLED && CONFIG_KERNEL_DEBUG */

/*
 * Check if there is a thread of higher prio than the current one. Should only
 * be called if we already know that the current thread is preemptible.
 */
int __must_switch_threads(void)
{
#ifdef CONFIG_PREEMPT_ENABLED
	K_DEBUG("current prio: %d, highest prio: %d\n",
		_current->base.prio, _get_highest_ready_prio());

#ifdef CONFIG_KERNEL_DEBUG
	_dump_ready_q();
#endif  /* CONFIG_KERNEL_DEBUG */

	return _is_prio_higher(_get_highest_ready_prio(), _current->base.prio);
#else
	return 0;
#endif
}

int  k_thread_priority_get(k_tid_t thread)
{
	return thread->base.prio;
}

void k_thread_priority_set(k_tid_t tid, int prio)
{
	/*
	 * Use NULL, since we cannot know what the entry point is (we do not
	 * keep track of it) and idle cannot change its priority.
	 */
	_ASSERT_VALID_PRIO(prio, NULL);
	__ASSERT(!_is_in_isr(), "");

	struct k_thread *thread = (struct k_thread *)tid;
	int key = irq_lock();

	_thread_priority_set(thread, prio);
	_reschedule_threads(key);
}

/*
 * Interrupts must be locked when calling this function.
 *
 * This function, along with _add_thread_to_ready_q() and
 * _remove_thread_from_ready_q(), are the _only_ places where a thread is
 * taken off or put on the ready queue.
 */
void _move_thread_to_end_of_prio_q(struct k_thread *thread)
{
#ifdef CONFIG_MULTITHREADING
	int q_index = _get_ready_q_q_index(thread->base.prio);
	sys_dlist_t *q = &_ready_q.q[q_index];

	if (sys_dlist_is_tail(q, &thread->base.k_q_node)) {
		return;
	}

	sys_dlist_remove(&thread->base.k_q_node);
	sys_dlist_append(q, &thread->base.k_q_node);

	struct k_thread **cache = &_ready_q.cache;

	*cache = *cache == thread ? _get_ready_q_head() : *cache;
#endif
}

void k_yield(void)
{
	__ASSERT(!_is_in_isr(), "");

	int key = irq_lock();

	_move_thread_to_end_of_prio_q(_current);

	if (_current == _get_next_ready_thread()) {
		irq_unlock(key);
#ifdef CONFIG_STACK_SENTINEL
		_check_stack_sentinel();
#endif
	} else {
		_Swap(key);
	}
}

void k_sleep(s32_t duration)
{
#ifdef CONFIG_MULTITHREADING
	/* volatile to guarantee that irq_lock() is executed after ticks is
	 * populated
	 */
	volatile s32_t ticks;
	unsigned int key;

	__ASSERT(!_is_in_isr(), "");
	__ASSERT(duration != K_FOREVER, "");

	K_DEBUG("thread %p for %d ns\n", _current, duration);

	/* wait of 0 ms is treated as a 'yield' */
	if (duration == 0) {
		k_yield();
		return;
	}

	ticks = _TICK_ALIGN + _ms_to_ticks(duration);
	key = irq_lock();

	_remove_thread_from_ready_q(_current);
	_add_thread_timeout(_current, NULL, ticks);

	_Swap(key);
#endif
}

void k_wakeup(k_tid_t thread)
{
	int key = irq_lock();

	/* verify first if thread is not waiting on an object */
	if (_is_thread_pending(thread)) {
		irq_unlock(key);
		return;
	}

	if (_abort_thread_timeout(thread) == _INACTIVE) {
		irq_unlock(key);
		return;
	}

	_ready_thread(thread);

	if (_is_in_isr()) {
		irq_unlock(key);
	} else {
		_reschedule_threads(key);
	}
}

k_tid_t k_current_get(void)
{
	return _current;
}

#ifdef CONFIG_TIMESLICING
extern s32_t _time_slice_duration;    /* Measured in ms */
extern s32_t _time_slice_elapsed;     /* Measured in ms */
extern int _time_slice_prio_ceiling;

void k_sched_time_slice_set(s32_t duration_in_ms, int prio)
{
	__ASSERT(duration_in_ms >= 0, "");
	__ASSERT((prio >= 0) && (prio < CONFIG_NUM_PREEMPT_PRIORITIES), "");

	_time_slice_duration = duration_in_ms;
	_time_slice_elapsed = 0;
	_time_slice_prio_ceiling = prio;
}

int _is_thread_time_slicing(struct k_thread *thread)
{
	/*
	 * Time slicing is done on the thread if following conditions are met
	 *
	 * Time slice duration should be set > 0
	 * Should not be the idle thread
	 * Priority should be higher than time slice priority ceiling
	 * There should be multiple threads active with same priority
	 */

	if (!(_time_slice_duration > 0) || (_is_idle_thread_ptr(thread))
	    || _is_prio_higher(thread->base.prio, _time_slice_prio_ceiling)) {
		return 0;
	}

	int q_index = _get_ready_q_q_index(thread->base.prio);
	sys_dlist_t *q = &_ready_q.q[q_index];

	return sys_dlist_has_multiple_nodes(q);
}

/* Must be called with interrupts locked */
/* Should be called only immediately before a thread switch */
void _update_time_slice_before_swap(void)
{
#ifdef CONFIG_TICKLESS_KERNEL
	if (!_is_thread_time_slicing(_get_next_ready_thread())) {
		return;
	}

	u32_t remaining = _get_remaining_program_time();

	if (!remaining || (_time_slice_duration < remaining)) {
		_set_time(_time_slice_duration);
	} else {
		/* Account previous elapsed time and reprogram
		 * timer with remaining time
		 */
		_set_time(remaining);
	}

#endif
	/* Restart time slice count at new thread switch */
	_time_slice_elapsed = 0;
}
#endif /* CONFIG_TIMESLICING */

int k_is_preempt_thread(void)
{
	return !_is_in_isr() && _is_preempt(_current);
}