sched: fair: Add strict skip buddy support

Skip buddy i.e task called yield() is always skipped and the
next entity is selected to run irrespective of the unfairness.

Change-Id: Ia9b9fbe46917152b58dc6406c718eb1cfb3b0fb2
Signed-off-by: Maria Yu <aiquny@codeaurora.org>

kernel/sched/fair.c

@@ -4247,7 +4247,8 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 				second = curr;
 		}
 
-		if (second && wakeup_preempt_entity(second, left) < 1)
+		if (second && (sched_feat(STRICT_SKIP_BUDDY) ||
+		    wakeup_preempt_entity(second, left) < 1))
 			se = second;
 	}
 

kernel/sched/features.h

@@ -26,6 +26,12 @@ SCHED_FEAT(NEXT_BUDDY, false)
  */
 SCHED_FEAT(LAST_BUDDY, true)
 
+/*
+ * skip buddy i.e task called yield() is always skipped and the
+ * next entity is selected to run irrespective of the vruntime
+ */
+SCHED_FEAT(STRICT_SKIP_BUDDY, true)
+
 /*
  * Consider buddies to be cache hot, decreases the likelyness of a
  * cache buddy being migrated away, increases cache locality.