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Message-Id: <1307561407-13809-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date: Wed, 8 Jun 2011 12:29:40 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
patches@...aro.org, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/28] 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@...ux.vnet.ibm.com>
---
kernel/rcutree.c | 65 +++++++++++++++-------------------------------
kernel/rcutree_plugin.h | 11 +-------
2 files changed, 22 insertions(+), 54 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 4cc6a94..36e79d2 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1634,6 +1634,20 @@ 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)
{
@@ -1646,12 +1660,14 @@ 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);
- kthread_bind(t, cpu);
+ 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;
}
@@ -1758,12 +1774,11 @@ 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.
*/
@@ -1771,30 +1786,18 @@ 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.
*/
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
@@ -2261,7 +2239,6 @@ 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);
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c8bff30..ea2e2fb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -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
--
1.7.3.2
--
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