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Commit 9a432736 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Simplify curing of load woes 



Make the functions creating the kthreads wake them up.  Leverage the
fact that the per-node and boost kthreads can run anywhere, thus
dispensing with the need to wake them up once the incoming CPU has
gone fully online.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarDaniel J Blueman <daniel.blueman@gmail.com>
parent 59c5f46f

kernel/rcutree.c

+21 −44
Original line number Diff line number Diff line
@@ -1635,6 +1635,20 @@ static int rcu_cpu_kthread(void *arg) 
 * to manipulate rcu_cpu_kthread_task.  There might be another CPU

 * attempting to access it during boot, but the locking in kthread_bind()

 * will enforce sufficient ordering.

 *

 * Please note that we cannot simply refuse to wake up the per-CPU

 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,

 * which can result in softlockup complaints if the task ends up being

 * idle for more than a couple of minutes.

 *

 * However, please note also that we cannot bind the per-CPU kthread to its

 * CPU until that CPU is fully online.  We also cannot wait until the

 * CPU is fully online before we create its per-CPU kthread, as this would

 * deadlock the system when CPU notifiers tried waiting for grace

 * periods.  So we bind the per-CPU kthread to its CPU only if the CPU

 * is online.  If its CPU is not yet fully online, then the code in

 * rcu_cpu_kthread() will wait until it is fully online, and then do

 * the binding.

 */

static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)

{
@@ -1647,12 +1661,14 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) 
	t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);

	if (IS_ERR(t))

		return PTR_ERR(t);

	if (cpu_online(cpu))

		kthread_bind(t, cpu);

	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;

	WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);

	per_cpu(rcu_cpu_kthread_task, cpu) = t;

	sp.sched_priority = RCU_KTHREAD_PRIO;

	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

	per_cpu(rcu_cpu_kthread_task, cpu) = t;

	wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */

	return 0;

}
@@ -1759,12 +1775,11 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, 
		raw_spin_unlock_irqrestore(&rnp->lock, flags);

		sp.sched_priority = 99;

		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

		wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */

	}

	return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);

}



static void rcu_wake_one_boost_kthread(struct rcu_node *rnp);



/*

 * Spawn all kthreads -- called as soon as the scheduler is running.

 */
@@ -1772,30 +1787,18 @@ static int __init rcu_spawn_kthreads(void) 
{

	int cpu;

	struct rcu_node *rnp;

	struct task_struct *t;



	rcu_kthreads_spawnable = 1;

	for_each_possible_cpu(cpu) {

		per_cpu(rcu_cpu_has_work, cpu) = 0;

		if (cpu_online(cpu)) {

		if (cpu_online(cpu))

			(void)rcu_spawn_one_cpu_kthread(cpu);

			t = per_cpu(rcu_cpu_kthread_task, cpu);

			if (t)

				wake_up_process(t);

		}

	}

	rnp = rcu_get_root(rcu_state);

	(void)rcu_spawn_one_node_kthread(rcu_state, rnp);

	if (rnp->node_kthread_task)

		wake_up_process(rnp->node_kthread_task);

	if (NUM_RCU_NODES > 1) {

		rcu_for_each_leaf_node(rcu_state, rnp) {

		rcu_for_each_leaf_node(rcu_state, rnp)

			(void)rcu_spawn_one_node_kthread(rcu_state, rnp);

			t = rnp->node_kthread_task;

			if (t)

				wake_up_process(t);

			rcu_wake_one_boost_kthread(rnp);

		}

	}

	return 0;

}
@@ -2220,31 +2223,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) 
	}

}



/*

 * kthread_create() creates threads in TASK_UNINTERRUPTIBLE state,

 * but the RCU threads are woken on demand, and if demand is low this

 * could be a while triggering the hung task watchdog.

 *

 * In order to avoid this, poke all tasks once the CPU is fully

 * up and running.

 */

static void __cpuinit rcu_online_kthreads(int cpu)

{

	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);

	struct rcu_node *rnp = rdp->mynode;

	struct task_struct *t;



	t = per_cpu(rcu_cpu_kthread_task, cpu);

	if (t)

		wake_up_process(t);



	t = rnp->node_kthread_task;

	if (t)

		wake_up_process(t);



	rcu_wake_one_boost_kthread(rnp);

}



/*

 * Handle CPU online/offline notification events.

 */
@@ -2262,7 +2240,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, 
		rcu_prepare_kthreads(cpu);

		break;

	case CPU_ONLINE:

		rcu_online_kthreads(cpu);

	case CPU_DOWN_FAILED:

		rcu_node_kthread_setaffinity(rnp, -1);

		rcu_cpu_kthread_setrt(cpu, 1);

kernel/rcutree_plugin.h

+1 −10
Original line number Diff line number Diff line
@@ -1299,15 +1299,10 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 
	raw_spin_unlock_irqrestore(&rnp->lock, flags);

	sp.sched_priority = RCU_KTHREAD_PRIO;

	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);

	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */

	return 0;

}



static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)

{

	if (rnp->boost_kthread_task)

		wake_up_process(rnp->boost_kthread_task);

}



#else /* #ifdef CONFIG_RCU_BOOST */



static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1331,10 +1326,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 
	return 0;

}



static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)

{

}



#endif /* #else #ifdef CONFIG_RCU_BOOST */



#ifndef CONFIG_SMP