kernel/timeslicing.c

/*
 * Copyright (c) 2018, 2024 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#include <zephyr/kernel.h>
#include <kswap.h>
#include <ksched.h>
#include <ipi.h>

static int slice_ticks = DIV_ROUND_UP(CONFIG_TIMESLICE_SIZE * Z_HZ_ticks, Z_HZ_ms);
static int slice_max_prio = CONFIG_TIMESLICE_PRIORITY;
static struct _timeout slice_timeouts[CONFIG_MP_MAX_NUM_CPUS];
static bool slice_expired[CONFIG_MP_MAX_NUM_CPUS];

#ifdef CONFIG_SWAP_NONATOMIC
/* If z_swap() isn't atomic, then it's possible for a timer interrupt
 * to try to timeslice away _current after it has already pended
 * itself but before the corresponding context switch.  Treat that as
 * a noop condition in z_time_slice().
 */
struct k_thread *pending_current;
#endif

static inline int slice_time(struct k_thread *thread)
{
	int ret = slice_ticks;

#ifdef CONFIG_TIMESLICE_PER_THREAD
	if (thread->base.slice_ticks != 0) {
		ret = thread->base.slice_ticks;
	}
#else
	ARG_UNUSED(thread);
#endif
	return ret;
}

bool thread_is_sliceable(struct k_thread *thread)
{
	bool ret = thread_is_preemptible(thread)
		&& slice_time(thread) != 0
		&& !z_is_prio_higher(thread->base.prio, slice_max_prio)
		&& !z_is_thread_prevented_from_running(thread)
		&& !z_is_idle_thread_object(thread);

#ifdef CONFIG_TIMESLICE_PER_THREAD
	ret |= thread->base.slice_ticks != 0;
#endif

	return ret;
}

static void slice_timeout(struct _timeout *timeout)
{
	int cpu = ARRAY_INDEX(slice_timeouts, timeout);

	slice_expired[cpu] = true;

	/* We need an IPI if we just handled a timeslice expiration
	 * for a different CPU.  Ideally this would be able to target
	 * the specific core, but that's not part of the API yet.
	 */
	if (IS_ENABLED(CONFIG_SMP) && cpu != _current_cpu->id) {
		flag_ipi();
	}
}

void z_reset_time_slice(struct k_thread *thread)
{
	int cpu = _current_cpu->id;

	z_abort_timeout(&slice_timeouts[cpu]);
	slice_expired[cpu] = false;
	if (thread_is_sliceable(thread)) {
		z_add_timeout(&slice_timeouts[cpu], slice_timeout,
			      K_TICKS(slice_time(thread) - 1));
	}
}

void k_sched_time_slice_set(int32_t slice, int prio)
{
	K_SPINLOCK(&_sched_spinlock) {
		slice_ticks = k_ms_to_ticks_ceil32(slice);
		slice_max_prio = prio;
		z_reset_time_slice(_current);
	}
}

#ifdef CONFIG_TIMESLICE_PER_THREAD
void k_thread_time_slice_set(struct k_thread *thread, int32_t thread_slice_ticks,
			     k_thread_timeslice_fn_t expired, void *data)
{
	K_SPINLOCK(&_sched_spinlock) {
		thread->base.slice_ticks = thread_slice_ticks;
		thread->base.slice_expired = expired;
		thread->base.slice_data = data;
	}
}
#endif

/* Called out of each timer interrupt */
void z_time_slice(void)
{
	k_spinlock_key_t key = k_spin_lock(&_sched_spinlock);
	struct k_thread *curr = _current;

#ifdef CONFIG_SWAP_NONATOMIC
	if (pending_current == curr) {
		z_reset_time_slice(curr);
		k_spin_unlock(&_sched_spinlock, key);
		return;
	}
	pending_current = NULL;
#endif

	if (slice_expired[_current_cpu->id] && thread_is_sliceable(curr)) {
#ifdef CONFIG_TIMESLICE_PER_THREAD
		if (curr->base.slice_expired) {
			k_spin_unlock(&_sched_spinlock, key);
			curr->base.slice_expired(curr, curr->base.slice_data);
			key = k_spin_lock(&_sched_spinlock);
		}
#endif
		if (!z_is_thread_prevented_from_running(curr)) {
			move_thread_to_end_of_prio_q(curr);
		}
		z_reset_time_slice(curr);
	}
	k_spin_unlock(&_sched_spinlock, key);
}