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: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Daniel J Blueman <daniel.blueman@gmail.com>
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@ -1635,6 +1635,20 @@ static int rcu_cpu_kthread(void *arg)
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* to manipulate rcu_cpu_kthread_task. There might be another CPU
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* to manipulate rcu_cpu_kthread_task. There might be another CPU
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* attempting to access it during boot, but the locking in kthread_bind()
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* attempting to access it during boot, but the locking in kthread_bind()
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* will enforce sufficient ordering.
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* will enforce sufficient ordering.
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*
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* Please note that we cannot simply refuse to wake up the per-CPU
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* kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
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* which can result in softlockup complaints if the task ends up being
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* idle for more than a couple of minutes.
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*
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* However, please note also that we cannot bind the per-CPU kthread to its
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* CPU until that CPU is fully online. We also cannot wait until the
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* CPU is fully online before we create its per-CPU kthread, as this would
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* deadlock the system when CPU notifiers tried waiting for grace
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* periods. So we bind the per-CPU kthread to its CPU only if the CPU
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* is online. If its CPU is not yet fully online, then the code in
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* rcu_cpu_kthread() will wait until it is fully online, and then do
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* the binding.
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*/
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*/
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static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
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static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
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{
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{
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@ -1647,12 +1661,14 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
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t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
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t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
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if (IS_ERR(t))
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if (IS_ERR(t))
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return PTR_ERR(t);
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return PTR_ERR(t);
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kthread_bind(t, cpu);
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if (cpu_online(cpu))
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kthread_bind(t, cpu);
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per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
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per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
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WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
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WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
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per_cpu(rcu_cpu_kthread_task, cpu) = t;
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sp.sched_priority = RCU_KTHREAD_PRIO;
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sp.sched_priority = RCU_KTHREAD_PRIO;
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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per_cpu(rcu_cpu_kthread_task, cpu) = t;
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wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
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return 0;
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return 0;
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}
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}
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@ -1759,12 +1775,11 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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sp.sched_priority = 99;
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sp.sched_priority = 99;
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
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}
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}
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return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
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return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
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}
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}
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static void rcu_wake_one_boost_kthread(struct rcu_node *rnp);
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/*
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/*
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* Spawn all kthreads -- called as soon as the scheduler is running.
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* Spawn all kthreads -- called as soon as the scheduler is running.
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*/
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*/
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@ -1772,30 +1787,18 @@ static int __init rcu_spawn_kthreads(void)
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{
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{
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int cpu;
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int cpu;
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struct rcu_node *rnp;
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struct rcu_node *rnp;
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struct task_struct *t;
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rcu_kthreads_spawnable = 1;
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rcu_kthreads_spawnable = 1;
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for_each_possible_cpu(cpu) {
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for_each_possible_cpu(cpu) {
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per_cpu(rcu_cpu_has_work, cpu) = 0;
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per_cpu(rcu_cpu_has_work, cpu) = 0;
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if (cpu_online(cpu)) {
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if (cpu_online(cpu))
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(void)rcu_spawn_one_cpu_kthread(cpu);
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(void)rcu_spawn_one_cpu_kthread(cpu);
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t = per_cpu(rcu_cpu_kthread_task, cpu);
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if (t)
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wake_up_process(t);
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}
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}
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}
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rnp = rcu_get_root(rcu_state);
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rnp = rcu_get_root(rcu_state);
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(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
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(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
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if (rnp->node_kthread_task)
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wake_up_process(rnp->node_kthread_task);
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if (NUM_RCU_NODES > 1) {
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if (NUM_RCU_NODES > 1) {
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rcu_for_each_leaf_node(rcu_state, rnp) {
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rcu_for_each_leaf_node(rcu_state, rnp)
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(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
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(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
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t = rnp->node_kthread_task;
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if (t)
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wake_up_process(t);
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rcu_wake_one_boost_kthread(rnp);
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}
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}
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}
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return 0;
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return 0;
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}
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}
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@ -2220,31 +2223,6 @@ static void __cpuinit rcu_prepare_kthreads(int cpu)
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}
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}
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}
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}
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/*
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* kthread_create() creates threads in TASK_UNINTERRUPTIBLE state,
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* but the RCU threads are woken on demand, and if demand is low this
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* could be a while triggering the hung task watchdog.
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*
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* In order to avoid this, poke all tasks once the CPU is fully
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* up and running.
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*/
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static void __cpuinit rcu_online_kthreads(int cpu)
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{
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struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
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struct rcu_node *rnp = rdp->mynode;
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struct task_struct *t;
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t = per_cpu(rcu_cpu_kthread_task, cpu);
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if (t)
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wake_up_process(t);
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t = rnp->node_kthread_task;
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if (t)
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wake_up_process(t);
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rcu_wake_one_boost_kthread(rnp);
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}
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/*
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/*
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* Handle CPU online/offline notification events.
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* Handle CPU online/offline notification events.
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*/
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*/
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@ -2262,7 +2240,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
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rcu_prepare_kthreads(cpu);
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rcu_prepare_kthreads(cpu);
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break;
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break;
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case CPU_ONLINE:
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case CPU_ONLINE:
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rcu_online_kthreads(cpu);
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case CPU_DOWN_FAILED:
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case CPU_DOWN_FAILED:
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rcu_node_kthread_setaffinity(rnp, -1);
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rcu_node_kthread_setaffinity(rnp, -1);
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rcu_cpu_kthread_setrt(cpu, 1);
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rcu_cpu_kthread_setrt(cpu, 1);
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@ -1299,15 +1299,10 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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sp.sched_priority = RCU_KTHREAD_PRIO;
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sp.sched_priority = RCU_KTHREAD_PRIO;
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
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wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
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return 0;
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return 0;
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}
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}
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static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
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{
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if (rnp->boost_kthread_task)
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wake_up_process(rnp->boost_kthread_task);
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}
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#else /* #ifdef CONFIG_RCU_BOOST */
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#else /* #ifdef CONFIG_RCU_BOOST */
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static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
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static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
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@ -1331,10 +1326,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
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return 0;
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return 0;
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}
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}
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static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
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{
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}
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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#ifndef CONFIG_SMP
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#ifndef CONFIG_SMP
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