[patch] BFS 421: fix try_preempt

[Hillf Danton]

We have to keep deadline latest, so no update if not checked.

Alternatively we could try preempt in the following way,

	rcu_read_lock();
	for_each_domain(task_cpu(q), sd) {
		for_each_cpu_and(cpu, tsk_cpus_allowed(p),
						sched_domain_span(sd)) {
			if (!cpu_online(cpu))
				continue;
			if (can_preempt(p, cpu_rq(cpu)->rq_prio,
						cpu_rq(cpu)->rq_deadline)) {
				resched_task(cpu_rq(cpu)->curr);
				goto out;
			}
		}
	}
out:
	rcu_read_unlock();


where the upside is that the LLC is invovled, and the downside is that we are
not sure the preempted task has the highest priority and the latest deadline.

What to do next?


--- a/kernel/sched/bfs.c	Wed Jun  6 20:14:36 2012
+++ b/kernel/sched/bfs.c	Wed Jun  6 20:16:48 2012
@@ -1452,10 +1452,11 @@ static void try_preempt(struct task_stru
 		if (rq_prio < highest_prio)
 			continue;

-		if (rq_prio > highest_prio ||
-		    deadline_after(rq->rq_deadline, latest_deadline)) {
+		if (rq_prio > highest_prio)
+			goto set;
+		if (deadline_after(rq->rq_deadline, latest_deadline)) {
 			latest_deadline = rq->rq_deadline;
-			highest_prio = rq_prio;
+set:			highest_prio = rq_prio;
 			highest_prio_rq = rq;
 		}
 	}
--
--
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