Function sched_idletd

freebsd/kern/sched_ule.c:2808–2887

* The actual idle process. */

 * The actual idle process.
 */
void
sched_idletd(void *dummy)
{
	struct thread *td;
	struct tdq *tdq;
	int oldswitchcnt, switchcnt;
	int i;

	mtx_assert(&Giant, MA_NOTOWNED);
	td = curthread;
	tdq = TDQ_SELF();
	THREAD_NO_SLEEPING();
	oldswitchcnt = -1;
	for (;;) {
		if (tdq->tdq_load) {
			thread_lock(td);
			mi_switch(SW_VOL | SWT_IDLE);
		}
		switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
#ifdef SMP
		if (always_steal || switchcnt != oldswitchcnt) {
			oldswitchcnt = switchcnt;
			if (tdq_idled(tdq) == 0)
				continue;
		}
		switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
#else
		oldswitchcnt = switchcnt;
#endif
		/*
		 * If we're switching very frequently, spin while checking
		 * for load rather than entering a low power state that 
		 * may require an IPI.  However, don't do any busy
		 * loops while on SMT machines as this simply steals
		 * cycles from cores doing useful work.
		 */
		if (TDQ_IDLESPIN(tdq) && switchcnt > sched_idlespinthresh) {
			for (i = 0; i < sched_idlespins; i++) {
				if (tdq->tdq_load)
					break;
				cpu_spinwait();
			}
		}

		/* If there was context switch during spin, restart it. */
		switchcnt = tdq->tdq_switchcnt + tdq->tdq_oldswitchcnt;
		if (tdq->tdq_load != 0 || switchcnt != oldswitchcnt)
			continue;

		/* Run main MD idle handler. */
		tdq->tdq_cpu_idle = 1;
		/*
		 * Make sure that tdq_cpu_idle update is globally visible
		 * before cpu_idle() read tdq_load.  The order is important
		 * to avoid race with tdq_notify.
		 */
		atomic_thread_fence_seq_cst();
		/*