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rcu: Simplify curing of load woes

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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>
This commit is contained in:
Paul E. McKenney 2011-05-30 20:38:55 -07:00
parent 59c5f46fbe
commit 9a43273690
2 changed files with 22 additions and 54 deletions
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63
kernel/rcutree.c
View file

@ -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);

11
kernel/rcutree_plugin.h
View file

@ -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