sched: Remove redundant update_runtime notifier

migration_call() will do all the things that update_runtime() does.
So let's remove it.

Furthermore, there is potential risk that the current code will catch
BUG_ON at line 689 of rt.c when do cpu hotplug while there are realtime
threads running because of enabling runtime twice while the rt_runtime
may already changed.

Signed-off-by: Neil Zhang <zhangwm@marvell.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1365685499-26515-1-git-send-email-zhangwm@marvell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -6285,9 +6285,6 @@ void __init sched_init_smp(void)
 	hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
 	hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
 
-	/* RT runtime code needs to handle some hotplug events */
-	hotcpu_notifier(update_runtime, 0);
-
 	init_hrtick();
 
 	/* Move init over to a non-isolated CPU */

kernel/sched/rt.c

@@ -699,15 +699,6 @@ balanced:
 	}
 }
 
-static void disable_runtime(struct rq *rq)
-{
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&rq->lock, flags);
-	__disable_runtime(rq);
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
-}
-
 static void __enable_runtime(struct rq *rq)
 {
 	rt_rq_iter_t iter;
@@ -732,37 +723,6 @@ static void __enable_runtime(struct rq *rq)
 	}
 }
 
-static void enable_runtime(struct rq *rq)
-{
-	unsigned long flags;
-
-	raw_spin_lock_irqsave(&rq->lock, flags);
-	__enable_runtime(rq);
-	raw_spin_unlock_irqrestore(&rq->lock, flags);
-}
-
-int update_runtime(struct notifier_block *nfb, unsigned long action, void *hcpu)
-{
-	int cpu = (int)(long)hcpu;
-
-	switch (action) {
-	case CPU_DOWN_PREPARE:
-	case CPU_DOWN_PREPARE_FROZEN:
-		disable_runtime(cpu_rq(cpu));
-		return NOTIFY_OK;
-
-	case CPU_DOWN_FAILED:
-	case CPU_DOWN_FAILED_FROZEN:
-	case CPU_ONLINE:
-	case CPU_ONLINE_FROZEN:
-		enable_runtime(cpu_rq(cpu));
-		return NOTIFY_OK;
-
-	default:
-		return NOTIFY_DONE;
-	}
-}
-
 static int balance_runtime(struct rt_rq *rt_rq)
 {
 	int more = 0;

kernel/sched/sched.h

@@ -1041,7 +1041,6 @@ static inline void idle_balance(int cpu, struct rq *rq)
 extern void sysrq_sched_debug_show(void);
 extern void sched_init_granularity(void);
 extern void update_max_interval(void);
-extern int update_runtime(struct notifier_block *nfb, unsigned long action, void *hcpu);
 extern void init_sched_rt_class(void);
 extern void init_sched_fair_class(void);