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, 8 insertions, 1 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e91eb050d2fb..90cc4b53cc5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2939,12 +2939,19 @@ pick_next_task(struct rq *rq)
         /*
          * 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(rq->nr_running == rq->cfs.h_nr_running)) {
                 p = fair_sched_class.pick_next_task(rq);
                 if (likely(p))
                         return p;
         }
+        */
 
         for_each_class(class) {
                 p = class->pick_next_task(rq);