sched: Warn on rt throttling

The default rt-throttling is a source of never ending questions. Warn
once when we go into throttling so folks have that info in dmesg.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1110051331480.18778@ionosSigned-off-by: NIngo Molnar <mingo@elte.hu>

kernel/sched_rt.c

@@ -655,6 +655,7 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 
 	if (rt_rq->rt_time > runtime) {
 		rt_rq->rt_throttled = 1;
+		printk_once(KERN_WARNING "sched: RT throttling activated\n");
 		if (rt_rq_throttled(rt_rq)) {
 			sched_rt_rq_dequeue(rt_rq);
 			return 1;