path: root/litmus/sched_edf_wm.c

/* EDF-WM: based on PSN-EDF.
 */

#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/spinlock.h>

#include <linux/module.h>

#include <litmus/litmus.h>
#include <litmus/jobs.h>
#include <litmus/sched_plugin.h>
#include <litmus/edf_common.h>

typedef struct {
	rt_domain_t 		domain;
	int          		cpu;
	struct task_struct* 	scheduled; /* only RT tasks */

	/* The enforcement timer is used to accurately police
	 * slice budgets. */
	struct hrtimer		enforcement_timer;
	int			timer_armed;
/*
 * scheduling lock slock
 * protects the domain and serializes scheduling decisions
 */
#define slock domain.ready_lock

} wm_domain_t;

DEFINE_PER_CPU(wm_domain_t, wm_domains);

#define TRACE_DOM(dom, fmt, args...) \
	TRACE("(wm_domains[%d]) " fmt, (dom)->cpu, ##args)


#define local_domain         (&__get_cpu_var(wm_domains))
#define remote_domain(cpu)   (&per_cpu(wm_domains, cpu))
#define domain_of_task(task) (remote_domain(get_partition(task)))
#define domain_from_timer(t) (container_of((t), wm_domain_t, enforcement_timer))

static int is_sliced_task(struct task_struct* t)
{
	return tsk_rt(t)->task_params.semi_part.wm.count;
}

static void compute_slice_params(struct task_struct* t)
{
	struct rt_param* p = tsk_rt(t);
	/* Here we do a little trick to make the generic EDF code
	 * play well with job slices. We overwrite the job-level
	 * release and deadline fields with the slice-specific values
	 * so that we can enqueue this task in an EDF rt_domain_t
	 * without issue. The actual values are cached in the semi_part.wm
	 * structure. */
	p->job_params.deadline = p->semi_part.wm.job_release +
		p->semi_part.wm.slice->deadline;
	p->job_params.release  = p->semi_part.wm.job_release +
		p->semi_part.wm.slice->offset;

	/* Similarly, we play a trick on the cpu field. */
	p->task_params.cpu = p->semi_part.wm.slice->cpu;

	/* update the per-slice budget reference */
	p->semi_part.wm.exec_time = p->job_params.exec_time;
}

static void complete_sliced_job(struct task_struct* t)
{
	struct rt_param* p = tsk_rt(t);

	/* We need to undo our trickery to the
	 * job parameters (see above). */
	p->job_params.release  = p->semi_part.wm.job_release;
	p->job_params.deadline = p->semi_part.wm.job_deadline;

	/* Ok, now let generic code do the actual work. */
	prepare_for_next_period(t);

	/* And finally cache the updated parameters. */
	p->semi_part.wm.job_release = p->job_params.release;
	p->semi_part.wm.job_deadline = p->job_params.deadline;
}

static void advance_next_slice(struct task_struct* t, int completion_signaled)
{
	int idx;
	struct rt_param* p = tsk_rt(t);

	/* make sure this is actually a sliced job */
	BUG_ON(!is_sliced_task(t));

	/* determine index of current slice */
	idx = p->semi_part.wm.slice -
		p->task_params.semi_part.wm.slices;

	if (completion_signaled)
		idx = 0;
	else
		/* increment and wrap around, if necessary */
		idx = (idx + 1) % p->task_params.semi_part.wm.count;

	/* point to next slice */
	p->semi_part.wm.slice =
		p->task_params.semi_part.wm.slices + idx;

	/* Check if we need to update essential job parameters. */
	if (!idx) {
		/* job completion */
		sched_trace_task_completion(t, !completion_signaled);
		complete_sliced_job(t);
	}

	/* Update job parameters for new slice. */
	compute_slice_params(t);
}

static int slice_budget_exhausted(struct task_struct* t)
{
	struct rt_param* p = tsk_rt(t);

	/* Compute how much execution time has been consumed
	 * since last slice advancement. */
	lt_t slice_exec = p->job_params.exec_time - p->semi_part.wm.exec_time;
	return slice_exec >= p->semi_part.wm.slice->budget;
}

/* we assume the lock is being held */
static void preempt(wm_domain_t *dom)
{
	TRACE_DOM(dom, "will be preempted.\n");
	/* We pass NULL as the task since non-preemptive sections are not
	 * supported in this plugin, so per-task checks are not needed. */
	preempt_if_preemptable(NULL, dom->cpu);
}

static enum hrtimer_restart on_enforcement_timeout(struct hrtimer *timer)
{
	wm_domain_t *dom = domain_from_timer(timer);
	unsigned long flags;

	raw_spin_lock_irqsave(&dom->slock, flags);
	if (likely(dom->timer_armed)) {
		TRACE_DOM(dom, "enforcement timer fired.\n");
		dom->timer_armed = 0;
		preempt(dom);
	} else
		TRACE_DOM(dom, "timer fired but not armed???\n");
	raw_spin_unlock_irqrestore(&dom->slock, flags);
	return  HRTIMER_NORESTART;
}

static void wm_domain_init(wm_domain_t* dom,
			   check_resched_needed_t check,
			   release_jobs_t release,
			   int cpu)
{
	edf_domain_init(&dom->domain, check, release);
	dom->cpu      		= cpu;
	dom->scheduled		= NULL;
	dom->timer_armed        = 0;
	hrtimer_init(&dom->enforcement_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	dom->enforcement_timer.function = on_enforcement_timeout;
}

static void requeue(struct task_struct* t, rt_domain_t *edf)
{
	if (t->state != TASK_RUNNING)
		TRACE_TASK(t, "requeue: !TASK_RUNNING\n");

	set_rt_flags(t, RT_F_RUNNING);
	if (is_released(t, litmus_clock()))
		__add_ready(edf, t);
	else
		add_release(edf, t); /* it has got to wait */
}

static int wm_check_resched(rt_domain_t *edf)
{
	wm_domain_t *dom = container_of(edf, wm_domain_t, domain);

	/* because this is a callback from rt_domain_t we already hold
	 * the necessary lock for the ready queue
	 */
	if (edf_preemption_needed(edf, dom->scheduled)) {
		preempt(dom);
		return 1;
	} else
		return 0;
}

static void regular_job_completion(struct task_struct* t, int forced)
{
	sched_trace_task_completion(t, forced);
	TRACE_TASK(t, "job_completion().\n");

	set_rt_flags(t, RT_F_SLEEP);
	prepare_for_next_period(t);
}

static void wm_job_or_slice_completion(struct task_struct* t,
				       int completion_signaled)
{
	if (is_sliced_task(t))
		advance_next_slice(t, completion_signaled);
	else
		regular_job_completion(t, !completion_signaled);
}

static int wm_budget_exhausted(struct task_struct* t)
{
	if (is_sliced_task(t))
		return slice_budget_exhausted(t);
	else
		return budget_exhausted(t);
}

static void wm_tick(struct task_struct *t)
{
	wm_domain_t *dom = local_domain;

	/* Check for inconsistency. We don't need the lock for this since
	 * ->scheduled is only changed in schedule, which obviously is not
	 *  executing in parallel on this CPU
	 */
	BUG_ON(is_realtime(t) && t != dom->scheduled);

	if (is_realtime(t) && budget_enforced(t) && wm_budget_exhausted(t)) {
		set_tsk_need_resched(t);
		TRACE_DOM(dom, "budget of %d exhausted in tick\n",
			  t->pid);
	}
}

static struct task_struct* wm_schedule(struct task_struct * prev)
{
	wm_domain_t*		dom = local_domain;
	rt_domain_t*		edf = &dom->domain;
	struct task_struct*	next;

	int 			out_of_time, sleep, preempt,
				exists, blocks, resched;

	raw_spin_lock(&dom->slock);

	/* sanity checking
	 * differently from gedf, when a task exits (dead)
	 * dom->schedule may be null and prev _is_ realtime
	 */
	BUG_ON(dom->scheduled && dom->scheduled != prev);
	BUG_ON(dom->scheduled && !is_realtime(prev));

	/* (0) Determine state */
	exists      = dom->scheduled != NULL;
	blocks      = exists && !is_running(dom->scheduled);
	out_of_time = exists
		&& budget_enforced(dom->scheduled)
		&& wm_budget_exhausted(dom->scheduled);
	sleep	    = exists && get_rt_flags(dom->scheduled) == RT_F_SLEEP;
	preempt     = edf_preemption_needed(edf, prev);

	/* If we need to preempt do so.
	 * The following checks set resched to 1 in case of special
	 * circumstances.
	 */
	resched = preempt;

	/* If a task blocks we have no choice but to reschedule.
	 */
	if (blocks)
		resched = 1;

	/* Any task that is preemptable and either exhausts its execution
	 * budget or wants to sleep completes. We may have to reschedule after
	 * this.
	 */
	if ((out_of_time || sleep) && !blocks) {
		wm_job_or_slice_completion(dom->scheduled, sleep);
		resched = 1;
	}

	/* The final scheduling decision. Do we need to switch for some reason?
	 * Switch if we are in RT mode and have no task or if we need to
	 * resched.
	 */
	next = NULL;
	if (resched || !exists) {
		if (dom->scheduled && !blocks)
			requeue(dom->scheduled, edf);
		next = __take_ready(edf);
	} else
		/* Only override Linux scheduler if we have a real-time task
		 * scheduled that needs to continue. */
		if (exists)
			next = prev;

	if (next) {
		TRACE_TASK(next, "scheduled at %llu\n", litmus_clock());
		set_rt_flags(next, RT_F_RUNNING);
	} else {
		TRACE("becoming idle at %llu\n", litmus_clock());
	}

	dom->scheduled = next;
	raw_spin_unlock(&dom->slock);

	return next;
}


/*	Prepare a task for running in RT mode
 */
static void wm_task_new(struct task_struct * t, int on_rq, int running)
{
	wm_domain_t* dom = domain_of_task(t);
	rt_domain_t* edf = &dom->domain;
	unsigned long flags;

	TRACE_TASK(t, "psn edf: task new, cpu = %d\n",
		   t->rt_param.task_params.cpu);

	/* setup job parameters */
	release_at(t, litmus_clock());

	/* The task should be running in the queue, otherwise signal
	 * code will try to wake it up with fatal consequences.
	 */
	raw_spin_lock_irqsave(&dom->slock, flags);
	if (running) {
		/* there shouldn't be anything else running at the time */
		BUG_ON(dom->scheduled);
		dom->scheduled = t;
	} else {
		requeue(t, edf);
		/* maybe we have to reschedule */
		preempt(dom);
	}
	raw_spin_unlock_irqrestore(&dom->slock, flags);
}

static void wm_task_wake_up(struct task_struct *task)
{
	unsigned long flags;
	wm_domain_t* dom = domain_of_task(task);
	rt_domain_t* edf = &dom->domain;
	lt_t now;

	TRACE_TASK(task, "wake_up at %llu\n", litmus_clock());
	raw_spin_lock_irqsave(&dom->slock, flags);
	BUG_ON(is_queued(task));

	now = litmus_clock();
	if (is_tardy(task, now)) {
		/* new sporadic release */
		release_at(task, now);
		sched_trace_task_release(task);
	}

	/* Only add to ready queue if it is not the currently-scheduled
	 * task. This could be the case if a task was woken up concurrently
	 * on a remote CPU before the executing CPU got around to actually
	 * de-scheduling the task, i.e., wake_up() raced with schedule()
	 * and won.
	 */
	if (dom->scheduled != task)
		requeue(task, edf);

	raw_spin_unlock_irqrestore(&dom->slock, flags);
	TRACE_TASK(task, "wake up done\n");
}

static void wm_task_block(struct task_struct *t)
{
	/* only running tasks can block, thus t is in no queue */
	TRACE_TASK(t, "block at %llu, state=%d\n", litmus_clock(), t->state);

	BUG_ON(!is_realtime(t));
	BUG_ON(is_queued(t));
}

static void wm_task_exit(struct task_struct * t)
{
	unsigned long flags;
	wm_domain_t* dom = domain_of_task(t);
	rt_domain_t* edf = &dom->domain;

	raw_spin_lock_irqsave(&dom->slock, flags);
	if (is_queued(t)) {
		/* dequeue */
		remove(edf, t);
	}
	if (dom->scheduled == t)
		dom->scheduled = NULL;

	TRACE_TASK(t, "RIP, now reschedule\n");

	preempt(dom);
	raw_spin_unlock_irqrestore(&dom->slock, flags);
}

static long wm_admit_task(struct task_struct* tsk)
{
	return task_cpu(tsk) == tsk->rt_param.task_params.cpu ? 0 : -EINVAL;
}

/*	Plugin object	*/
static struct sched_plugin edf_wm_plugin __cacheline_aligned_in_smp = {
	.plugin_name		= "EDF-WM",
#ifdef CONFIG_SRP
	.srp_active		= 1,
#endif
	.tick			= wm_tick,
	.task_new		= wm_task_new,
	.complete_job		= complete_job,
	.task_exit		= wm_task_exit,
	.schedule		= wm_schedule,
	.task_wake_up		= wm_task_wake_up,
	.task_block		= wm_task_block,
	.admit_task		= wm_admit_task
};


static int __init init_edf_wm(void)
{
	int i;

	/* We do not really want to support cpu hotplug, do we? ;)
	 * However, if we are so crazy to do so,
	 * we cannot use num_online_cpu()
	 */
	for (i = 0; i < num_online_cpus(); i++) {
		wm_domain_init(remote_domain(i),
			       wm_check_resched,
			       NULL, i);
	}
	return register_sched_plugin(&edf_wm_plugin);
}

module_init(init_edf_wm);