Function sched_thread_priority

freebsd/kern/sched_ule.c:1748–1797

* Adjust the priority of a thread. Move it to the appropriate run-queue * if necessary. This is the back-end for several priority related * functions. */

 * functions.
 */
static void
sched_thread_priority(struct thread *td, u_char prio)
{
	struct td_sched *ts;
	struct tdq *tdq;
	int oldpri;

	KTR_POINT3(KTR_SCHED, "thread", sched_tdname(td), "prio",
	    "prio:%d", td->td_priority, "new prio:%d", prio,
	    KTR_ATTR_LINKED, sched_tdname(curthread));
	SDT_PROBE3(sched, , , change__pri, td, td->td_proc, prio);
	if (td != curthread && prio < td->td_priority) {
		KTR_POINT3(KTR_SCHED, "thread", sched_tdname(curthread),
		    "lend prio", "prio:%d", td->td_priority, "new prio:%d",
		    prio, KTR_ATTR_LINKED, sched_tdname(td));
		SDT_PROBE4(sched, , , lend__pri, td, td->td_proc, prio, 
		    curthread);
	} 
	ts = td_get_sched(td);
	THREAD_LOCK_ASSERT(td, MA_OWNED);
	if (td->td_priority == prio)
		return;
	/*
	 * If the priority has been elevated due to priority
	 * propagation, we may have to move ourselves to a new
	 * queue.  This could be optimized to not re-add in some
	 * cases.
	 */
	if (TD_ON_RUNQ(td) && prio < td->td_priority) {
		sched_rem(td);
		td->td_priority = prio;
		sched_add(td, SRQ_BORROWING | SRQ_HOLDTD);
		return;
	}
	/*
	 * If the thread is currently running we may have to adjust the lowpri
	 * information so other cpus are aware of our current priority.
	 */
	if (TD_IS_RUNNING(td)) {
		tdq = TDQ_CPU(ts->ts_cpu);
		oldpri = td->td_priority;
		td->td_priority = prio;
		if (prio < tdq->tdq_lowpri)
			tdq->tdq_lowpri = prio;
		else if (tdq->tdq_lowpri == oldpri)
			tdq_setlowpri(tdq, td);
		return;
	}
	td->td_priority = prio;
}

/*
 * Update a thread's priority when it is lent another thread's