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Commit e3995a25 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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rcu: put per-CPU kthread at non-RT priority during CPU hotplug operations 



If you are doing CPU hotplug operations, it is best not to have
CPU-bound realtime tasks running CPU-bound on the outgoing CPU.
So this commit makes per-CPU kthreads run at non-realtime priority
during that time.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 0f962a5e

kernel/rcutree.c

+26 −0
Original line number Diff line number Diff line
@@ -1463,6 +1463,30 @@ static void invoke_rcu_node_kthread(struct rcu_node *rnp) 
		wake_up_process(t);

}



/*

 * Set the specified CPU's kthread to run RT or not, as specified by

 * the to_rt argument.  The CPU-hotplug locks are held, so the task

 * is not going away.

 */

static void rcu_cpu_kthread_setrt(int cpu, int to_rt)

{

	int policy;

	struct sched_param sp;

	struct task_struct *t;



	t = per_cpu(rcu_cpu_kthread_task, cpu);

	if (t == NULL)

		return;

	if (to_rt) {

		policy = SCHED_FIFO;

		sp.sched_priority = RCU_KTHREAD_PRIO;

	} else {

		policy = SCHED_NORMAL;

		sp.sched_priority = 0;

	}

	sched_setscheduler_nocheck(t, policy, &sp);

}



/*

 * Timer handler to initiate the waking up of per-CPU kthreads that

 * have yielded the CPU due to excess numbers of RCU callbacks.
@@ -2166,9 +2190,11 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, 
	case CPU_ONLINE:

	case CPU_DOWN_FAILED:

		rcu_node_kthread_setaffinity(rnp, -1);

		rcu_cpu_kthread_setrt(cpu, 1);

		break;

	case CPU_DOWN_PREPARE:

		rcu_node_kthread_setaffinity(rnp, cpu);

		rcu_cpu_kthread_setrt(cpu, 0);

		break;

	case CPU_DYING:

	case CPU_DYING_FROZEN: