[RFC] sched: use plist in pulling RT task

[Hillf Danton]

Hi Steven

It is pushable tasks that are pulled, and they are maintained by runqueue with
plist, so the plist can be also used by puller for free.

Thanks

Hillf
---
 kernel/sched_rt.c |   35 ++++++++++++++++++++++-------------
 1 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index b03cd89..f4eecf9 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1471,6 +1471,7 @@ static int pull_rt_task(struct rq *this_rq)
 	int this_cpu = this_rq->cpu, ret = 0, cpu;
 	struct task_struct *p;
 	struct rq *src_rq;
+	int pulled_prio = MAX_RT_PRIO;

 	if (likely(!rt_overloaded(this_rq)))
 		return 0;
@@ -1481,6 +1482,8 @@ static int pull_rt_task(struct rq *this_rq)

 		src_rq = cpu_rq(cpu);

+		if (src_rq->rt.highest_prio.next >= pulled_prio)
+			continue;
 		/*
 		 * Don't bother taking the src_rq->lock if the next highest
 		 * task is known to be lower-priority than our current task.
@@ -1502,18 +1505,19 @@ static int pull_rt_task(struct rq *this_rq)
 		/*
 		 * Are there still pullable RT tasks?
 		 */
-		if (src_rq->rt.rt_nr_running <= 1)
+		if (! has_pushable_tasks(src_rq))
 			goto skip;

-		p = pick_next_highest_task_rt(src_rq, this_cpu);
-
 		/*
 		 * Do we have an RT task that preempts
 		 * the to-be-scheduled task?
 		 */
-		if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
-			WARN_ON(p == src_rq->curr);
-			WARN_ON(!p->on_rq);
+		plist_for_each_entry(p, &src_rq->rt.pushable_tasks,
+						    pushable_tasks) {
+			if (p->prio >= pulled_prio)
+				break;
+			if (! (p->prio < this_rq->rt.highest_prio.curr))
+				break;

 			/*
 			 * There's a chance that p is higher in priority
@@ -1524,22 +1528,27 @@ static int pull_rt_task(struct rq *this_rq)
 			 * current task on the run queue
 			 */
 			if (p->prio < src_rq->curr->prio)
-				goto skip;
+				continue;
+
+			if (! cpumask_test_cpu(this_cpu, &p->cpus_allowed))
+				continue;

+			pulled_prio = p->prio;
 			ret = 1;

 			deactivate_task(src_rq, p, 0);
 			set_task_cpu(p, this_cpu);
 			activate_task(this_rq, p, 0);
-			/*
-			 * We continue with the search, just in
-			 * case there's an even higher prio task
-			 * in another runqueue. (low likelihood
-			 * but possible)
-			 */
+			break;
 		}
 skip:
 		double_unlock_balance(this_rq, src_rq);
+		/*
+		 * We continue with the search, just in
+		 * case there's an even higher prio task
+		 * in another runqueue. (low likelihood
+		 * but possible)
+		 */
 	}

 	return ret;
--
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