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rcu: Remove waitqueue usage for cpu, node, and boost kthreads

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It is not necessary to use waitqueues for the RCU kthreads because
we always know exactly which thread is to be awakened.  In addition,
wake_up() only issues an actual wakeup when there is a thread waiting on
the queue, which was why there was an extra explicit wake_up_process()
to get the RCU kthreads started.

Eliminating the waitqueues (and wake_up()) in favor of wake_up_process()
eliminates the need for the initial wake_up_process() and also shrinks
the data structure size a bit.  The wakeup logic is placed in a new
rcu_wait() macro.

Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2011-05-20 16:06:29 -07:00 • committed by Ingo Molnar
commit 08bca60a69
3 changed files with 17 additions and 39 deletions
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23
kernel/rcutree.c
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@ -95,7 +95,6 @@ static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
DEFINE_PER_CPU(char, rcu_cpu_has_work);
static char rcu_kthreads_spawnable;
@ -1476,7 +1475,7 @@ static void invoke_rcu_cpu_kthread(void)
local_irq_restore(flags);
return;
}
wake_up(&__get_cpu_var(rcu_cpu_wq));
wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
local_irq_restore(flags);
}
@ -1596,14 +1595,12 @@ static int rcu_cpu_kthread(void *arg)
unsigned long flags;
int spincnt = 0;
unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
char work;
char *workp = &per_cpu(rcu_cpu_has_work, cpu);
for (;;) {
*statusp = RCU_KTHREAD_WAITING;
wait_event_interruptible(*wqp,
*workp != 0 || kthread_should_stop());
rcu_wait(*workp != 0 || kthread_should_stop());
local_bh_disable();
if (rcu_cpu_kthread_should_stop(cpu)) {
local_bh_enable();
@ -1654,7 +1651,6 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int 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;
wake_up_process(t);
sp.sched_priority = RCU_KTHREAD_PRIO;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
return 0;
@ -1677,8 +1673,7 @@ static int rcu_node_kthread(void *arg)
for (;;) {
rnp->node_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->node_wq,
atomic_read(&rnp->wakemask) != 0);
rcu_wait(atomic_read(&rnp->wakemask) != 0);
rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
raw_spin_lock_irqsave(&rnp->lock, flags);
mask = atomic_xchg(&rnp->wakemask, 0);
@ -1762,7 +1757,6 @@ static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->node_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
wake_up_process(t);
sp.sched_priority = 99;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
@ -1779,21 +1773,16 @@ static int __init rcu_spawn_kthreads(void)
rcu_kthreads_spawnable = 1;
for_each_possible_cpu(cpu) {
init_waitqueue_head(&per_cpu(rcu_cpu_wq, cpu));
per_cpu(rcu_cpu_has_work, cpu) = 0;
if (cpu_online(cpu))
(void)rcu_spawn_one_cpu_kthread(cpu);
}
rnp = rcu_get_root(rcu_state);
init_waitqueue_head(&rnp->node_wq);
rcu_init_boost_waitqueue(rnp);
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
if (NUM_RCU_NODES > 1)
rcu_for_each_leaf_node(rcu_state, rnp) {
init_waitqueue_head(&rnp->node_wq);
rcu_init_boost_waitqueue(rnp);
if (NUM_RCU_NODES > 1) {
rcu_for_each_leaf_node(rcu_state, rnp)
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
}
}
return 0;
}
early_initcall(rcu_spawn_kthreads);