/*
* Select the KSE that will be run next. From that find the thread, and
* remove it from the KSEGRP's run queue. If there is thread clustering,
* this will be what does it.
*/
struct thread *
choosethread(void)
{
struct kse *ke;
struct thread *td;
struct ksegrp *kg;
#if defined(SMP) && (defined(__i386__) || defined(__amd64__))
if (smp_active == 0 && PCPU_GET(cpuid) != 0) {
/* Shutting down, run idlethread on AP's */
td = PCPU_GET(idlethread);
ke = td->td_kse;
CTR1(KTR_RUNQ, "choosethread: td=%p (idle)", td);
ke->ke_flags |= KEF_DIDRUN;
TD_SET_RUNNING(td);
return (td);
}
#endif
retry:
ke = sched_choose();
if (ke) {
td = ke->ke_thread;
KASSERT((td->td_kse == ke), ("kse/thread mismatch"));
kg = ke->ke_ksegrp;
if (td->td_proc->p_flag & P_HADTHREADS) {
if (kg->kg_last_assigned == td) {
kg->kg_last_assigned = TAILQ_PREV(td,
threadqueue, td_runq);
}
TAILQ_REMOVE(&kg->kg_runq, td, td_runq);
kg->kg_runnable--;
}
CTR2(KTR_RUNQ, "choosethread: td=%p pri=%d",
td, td->td_priority);
} else {
/* Simulate runq_choose() having returned the idle thread */
td = PCPU_GET(idlethread);
ke = td->td_kse;
CTR1(KTR_RUNQ, "choosethread: td=%p (idle)", td);
}
ke->ke_flags |= KEF_DIDRUN;
/*
* If we are in panic, only allow system threads,
* plus the one we are running in, to be run.
*/
if (panicstr && ((td->td_proc->p_flag & P_SYSTEM) == 0 &&
(td->td_flags & TDF_INPANIC) == 0)) {
/* note that it is no longer on the run queue */
TD_SET_CAN_RUN(td);
goto retry;
}
TD_SET_RUNNING(td);
return (td);
}
void sched_schedule() {
// find a thread to schedule. the scheduled thread is removed from the
// queue, and the currently-run thread is re-added to the queue.
spl_lock(&_sched_lock);
thread_t* old = thr_current();
if(old) {
switch(old->state) {
case Runnable:
// don't stop if the thread still has time!
if(old->preempt_at > systime()) {
goto done;
}
break;
case Yielded:
// timeslice is given up.
old->state = Runnable;
break;
default:
// not relevant here.
break;
}
}
// BUG: this algorithm will start to choose the idle thread when
// only one other thread is remaining runnable.
thread_t* thr = sched_choose(old);
if(thr) {
trace("switching: %d:%d (%d)\n", thr->parent->id, thr->id, thr->priority);
thr->preempt_at = systime() + SCHED_TIMESLICE_US;
thr_switch(thr);
sched_remove_unlocked(thr);
if(old)
sched_add_unlocked(old);
goto done;
}
// let things stay as they are if only one thread exists.
if(old->state == Runnable) {
goto done;
}
fatal("no thread left to schedule - this is bad!\n");
done:
spl_unlock(&_sched_lock);
}
void sched_switch(thread_t *newtd) {
if (!sched_active)
return;
cs_enter();
thread_t *td = thread_self();
td->td_flags &= ~(TDF_SLICEEND | TDF_NEEDSWITCH);
if (td->td_state == TDS_RUNNING)
sched_add(td);
if (newtd == NULL)
newtd = sched_choose();
newtd->td_state = TDS_RUNNING;
cs_leave();
if (td != newtd)
ctx_switch(td, newtd);
}