Hook into SCHED_DEADLINE to protect LITMUS^RT tasks

SCHED_DEADLINE should not preempt LITMUS^RT tasks, as the LITMUS^RT
scheduling class is positioned above the SCHED_DEADLINE policy.

1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index c95c5122b105..f27f6f2b9f31 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -16,6 +16,8 @@
  */
 #include "sched.h"
 
+#include <litmus/litmus.h>
+
 #include <linux/slab.h>
 
 struct dl_bandwidth def_dl_bandwidth;
@@ -650,15 +652,17 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
         enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
         if (dl_task(rq->curr))
                 check_preempt_curr_dl(rq, p, 0);
-        else
+        else if (!is_realtime(rq->curr))
                 resched_curr(rq);
 
 #ifdef CONFIG_SMP
         /*
          * Queueing this task back might have overloaded rq, check if we need
          * to kick someone away.
+         *
+         * LITMUS^RT: don't incur this overhead if we are running a L^RT task.
          */
-        if (has_pushable_dl_tasks(rq)) {
+        if (has_pushable_dl_tasks(rq) && !is_realtime(rq->curr)) {
                 /*
                  * Nothing relies on rq->lock after this, so its safe to drop
                  * rq->lock.
@@ -1699,8 +1703,11 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
          * Since this might be the only -deadline task on the rq,
          * this is the right place to try to pull some other one
          * from an overloaded cpu, if any.
+         *
+         * LITMUS^RT: also don't pull tasks when we are running L^RT tasks.
          */
-        if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
+        if (!task_on_rq_queued(p) || rq->dl.dl_nr_running
+            || is_realtime(rq->curr))
                 return;
 
         queue_pull_task(rq);
@@ -1714,7 +1721,7 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 {
 
         /* If p is not queued we will update its parameters at next wakeup. */
-        if (!task_on_rq_queued(p))
+        if (!task_on_rq_queued(p) || is_realtime(rq->curr))
                 return;
 
         /*