Disable cut-to-CFS optimization in Linux scheduler

Global plugins require that the plugin be called even if there
currently is no real-time task executing on the local core.

1 files changed, 11 insertions, 3 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 42b4e32ec494..426f4e776188 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2697,21 +2697,29 @@ pick_next_task(struct rq *rq, struct task_struct *prev)
         /*
          * Optimization: we know that if all tasks are in
          * the fair class we can call that function directly:
-         */
+
+         * NOT IN LITMUS^RT!
+
+         * This breaks many assumptions in the plugins.
+         * Do not uncomment without thinking long and hard
+         * about how this affects global plugins such as GSN-EDF.
+
         if (likely(prev->sched_class == class &&
                    rq->nr_running == rq->cfs.h_nr_running)) {
                 p = fair_sched_class.pick_next_task(rq, prev);
                 if (unlikely(p == RETRY_TASK))
                         goto again;
 
-                /* assumes fair_sched_class->next == idle_sched_class */
+                // assumes fair_sched_class->next == idle_sched_class
                 if (unlikely(!p))
                         p = idle_sched_class.pick_next_task(rq, prev);
 
                 return p;
-        }
+
+        */
 
 again:
+
         for_each_class(class) {
                 p = class->pick_next_task(rq, prev);
                 if (p) {