sched: Disable TTWU_QUEUE on RT

The queued remote wakeup mechanism can introduce rather large
latencies if the number of migrated tasks is high. Disable it for RT.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched/features.h

@@ -46,11 +46,16 @@ SCHED_FEAT(DOUBLE_TICK, false)
  */
 SCHED_FEAT(NONTASK_CAPACITY, true)
 
+#ifdef CONFIG_PREEMPT_RT
+SCHED_FEAT(TTWU_QUEUE, false)
+#else
+
 /*
  * Queue remote wakeups on the target CPU and process them
  * using the scheduler IPI. Reduces rq->lock contention/bounces.
  */
 SCHED_FEAT(TTWU_QUEUE, true)
+#endif
 
 /*
  * When doing wakeups, attempt to limit superfluous scans of the LLC domain.