void xnclock_core_local_shot(struct xnsched *sched)
{
struct xntimerdata *tmd;
struct xntimer *timer;
xnsticks_t delay;
xntimerq_it_t it;
xntimerh_t *h;
/*
* Do not reprogram locally when inside the tick handler -
* will be done on exit anyway. Also exit if there is no
* pending timer.
*/
if (sched->status & XNINTCK)
return;
tmd = xnclock_this_timerdata(&nkclock);
h = xntimerq_it_begin(&tmd->q, &it);
if (h == NULL)
return;
/*
* Here we try to defer the host tick heading the timer queue,
* so that it does not preempt a real-time activity uselessly,
* in two cases:
*
* 1) a rescheduling is pending for the current CPU. We may
* assume that a real-time thread is about to resume, so we
* want to move the host tick out of the way until the host
* kernel resumes, unless there is no other outstanding
* timers.
*
* 2) the current thread is running in primary mode, in which
* case we may also defer the host tick until the host kernel
* resumes.
*
* The host tick deferral is cleared whenever Xenomai is about
* to yield control to the host kernel (see __xnsched_run()),
* or a timer with an earlier timeout date is scheduled,
* whichever comes first.
*/
sched->lflags &= ~XNHDEFER;
timer = container_of(h, struct xntimer, aplink);
if (unlikely(timer == &sched->htimer)) {
if (xnsched_resched_p(sched) ||
!xnthread_test_state(sched->curr, XNROOT)) {
h = xntimerq_it_next(&tmd->q, &it, h);
if (h) {
sched->lflags |= XNHDEFER;
timer = container_of(h, struct xntimer, aplink);
}
}
}
/**
* @fn int xnsched_run(void)
* @brief The rescheduling procedure.
*
* This is the central rescheduling routine which should be called to
* validate and apply changes which have previously been made to the
* nucleus scheduling state, such as suspending, resuming or changing
* the priority of threads. This call performs context switches as
* needed. xnsched_run() schedules out the current thread if:
*
* - the current thread is about to block.
* - a runnable thread from a higher priority scheduling class is
* waiting for the CPU.
* - the current thread does not lead the runnable threads from its
* own scheduling class (i.e. round-robin).
*
* The Cobalt core implements a lazy rescheduling scheme so that most
* of the services affecting the threads state MUST be followed by a
* call to the rescheduling procedure for the new scheduling state to
* be applied.
*
* In other words, multiple changes on the scheduler state can be done
* in a row, waking threads up, blocking others, without being
* immediately translated into the corresponding context switches.
* When all changes have been applied, xnsched_run() should be called
* for considering those changes, and possibly switching context.
*
* As a notable exception to the previous principle however, every
* action which ends up suspending the current thread begets an
* implicit call to the rescheduling procedure on behalf of the
* blocking service.
*
* Typically, self-suspension or sleeping on a synchronization object
* automatically leads to a call to the rescheduling procedure,
* therefore the caller does not need to explicitly issue
* xnsched_run() after such operations.
*
* The rescheduling procedure always leads to a null-effect if it is
* called on behalf of an interrupt service routine. Any outstanding
* scheduler lock held by the outgoing thread will be restored when
* the thread is scheduled back in.
*
* Calling this procedure with no applicable context switch pending is
* harmless and simply leads to a null-effect.
*
* @return Non-zero is returned if a context switch actually happened,
* otherwise zero if the current thread was left running.
*
* @coretags{unrestricted}
*/
static inline int test_resched(struct xnsched *sched)
{
int resched = xnsched_resched_p(sched);
#ifdef CONFIG_SMP
/* Send resched IPI to remote CPU(s). */
if (unlikely(!cpus_empty(sched->resched))) {
smp_mb();
ipipe_send_ipi(IPIPE_RESCHEDULE_IPI, sched->resched);
cpus_clear(sched->resched);
}
#endif
sched->status &= ~XNRESCHED;
return resched;
}
void xntimer_next_local_shot(xnsched_t *sched)
{
struct xntimer *timer;
xnsticks_t delay;
xntimerq_it_t it;
xntimerh_t *h;
/*
* Do not reprogram locally when inside the tick handler -
* will be done on exit anyway. Also exit if there is no
* pending timer.
*/
if (testbits(sched->status, XNINTCK))
return;
h = xntimerq_it_begin(&sched->timerqueue, &it);
if (h == NULL)
return;
/*
* Here we try to defer the host tick heading the timer queue,
* so that it does not preempt a real-time activity uselessly,
* in two cases:
*
* 1) a rescheduling is pending for the current CPU. We may
* assume that a real-time thread is about to resume, so we
* want to move the host tick out of the way until the host
* kernel resumes, unless there is no other outstanding
* timers.
*
* 2) the current thread is running in primary mode, in which
* case we may also defer the host tick until the host kernel
* resumes.
*
* The host tick deferral is cleared whenever Xenomai is about
* to yield control to the host kernel (see
* __xnpod_schedule()), or a timer with an earlier timeout
* date is scheduled, whichever comes first.
*/
__clrbits(sched->lflags, XNHDEFER);
timer = aplink2timer(h);
if (unlikely(timer == &sched->htimer)) {
if (xnsched_resched_p(sched) ||
!xnthread_test_state(sched->curr, XNROOT)) {
h = xntimerq_it_next(&sched->timerqueue, &it, h);
if (h) {
__setbits(sched->lflags, XNHDEFER);
timer = aplink2timer(h);
}
}
}
delay = xntimerh_date(&timer->aplink) -
(xnarch_get_cpu_tsc() + nklatency);
if (delay < 0)
delay = 0;
else if (delay > ULONG_MAX)
delay = ULONG_MAX;
xnarch_trace_tick((unsigned)delay);
xnarch_program_timer_shot(delay);
}
