/*
* Generic function to trigger preemption on either local or remote cpu
* from scheduler plugins. The key feature is that this function is
* non-preemptive section aware and does not invoke the scheduler / send
* IPIs if the to-be-preempted task is actually non-preemptive.
*/
void preempt_if_preemptable(struct task_struct* t, int cpu)
{
/* t is the real-time task executing on CPU on_cpu If t is NULL, then
* on_cpu is currently scheduling background work.
*/
int reschedule = 0;
if (!t)
/* move non-real-time task out of the way */
reschedule = 1;
else {
if (smp_processor_id() == cpu) {
/* local CPU case */
/* check if we need to poke userspace */
if (is_user_np(t))
/* Yes, poke it. This doesn't have to be atomic since
* the task is definitely not executing. */
request_exit_np(t);
else if (!is_kernel_np(t))
/* only if we are allowed to preempt the
* currently-executing task */
reschedule = 1;
} else {
/* Remote CPU case. Only notify if it's not a kernel
* NP section and if we didn't set the userspace
* flag. */
reschedule = !(is_kernel_np(t) || request_exit_np_atomic(t));
}
}
if (likely(reschedule))
litmus_reschedule(cpu);
}
static enum hrtimer_restart psnedf_simple_on_exhausted(struct task_struct *t, int in_schedule)
{
/* Assumption: t is scheduled on the CPU executing this callback */
if (budget_signalled(t) && !bt_flag_is_set(t, BTF_SIG_BUDGET_SENT)) {
/* signal exhaustion */
send_sigbudget(t); /* will set BTF_SIG_BUDGET_SENT */
}
if (budget_enforced(t) && !bt_flag_test_and_set(t, BTF_BUDGET_EXHAUSTED)) {
if (!is_np(t)) {
/* np tasks will be preempted when they become
* preemptable again
*/
litmus_reschedule_local();
TRACE("%d is preemptable => FORCE_RESCHED\n", t->pid);
} else if (is_user_np(t)) {
TRACE("%d is non-preemptable, preemption delayed.\n", t->pid);
request_exit_np(t);
}
}
return HRTIMER_NORESTART;
}
static struct task_struct* psnedf_schedule(struct task_struct * prev)
{
psnedf_domain_t* pedf = local_pedf;
rt_domain_t* edf = &pedf->domain;
struct task_struct* next;
int out_of_time, sleep, preempt,
np, exists, blocks, resched;
raw_readyq_lock(&pedf->slock);
/* sanity checking
* differently from gedf, when a task exits (dead)
* pedf->schedule may be null and prev _is_ realtime
*/
BUG_ON(pedf->scheduled && pedf->scheduled != prev);
BUG_ON(pedf->scheduled && !is_realtime(prev));
/* (0) Determine state */
exists = pedf->scheduled != NULL;
blocks = exists && !is_running(pedf->scheduled);
out_of_time = exists &&
budget_enforced(pedf->scheduled) &&
bt_flag_is_set(pedf->scheduled, BTF_BUDGET_EXHAUSTED);
np = exists && is_np(pedf->scheduled);
sleep = exists && is_completed(pedf->scheduled);
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;
/* Do budget stuff */
if (blocks)
budget_state_machine(prev,on_blocked);
else if (sleep)
budget_state_machine(prev,on_sleep);
else if (preempt)
budget_state_machine(prev,on_preempt);
/* If a task blocks we have no choice but to reschedule.
*/
if (blocks)
resched = 1;
/* Request a sys_exit_np() call if we would like to preempt but cannot.
* Multiple calls to request_exit_np() don't hurt.
*/
if (np && (out_of_time || preempt || sleep))
request_exit_np(pedf->scheduled);
/* Any task that is preemptable and either exhausts its execution
* budget or wants to sleep completes. We may have to reschedule after
* this.
*/
if (!np && (out_of_time || sleep) && !blocks) {
job_completion(pedf->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 ((!np || blocks) && (resched || !exists)) {
/* When preempting a task that does not block, then
* re-insert it into either the ready queue or the
* release queue (if it completed). requeue() picks
* the appropriate queue.
*/
if (pedf->scheduled && !blocks)
requeue(pedf->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());
} else {
TRACE("becoming idle at %llu\n", litmus_clock());
}
pedf->scheduled = next;
sched_state_task_picked();
raw_readyq_unlock(&pedf->slock);
return next;
}
