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rcu: Improve RCU-tasks energy efficiency

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The current RCU-tasks implementation uses strict polling to detect
callback arrivals.  This works quite well, but is not so good for
energy efficiency.  This commit therefore replaces the strict polling
with a wait queue.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2014-07-28 14:39:25 -07:00
parent 52db30ab23
commit c7b24d2b9a
1 changed files with 12 additions and 2 deletions
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14
kernel/rcu/update.c
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@ -365,6 +365,7 @@ early_initcall(check_cpu_stall_init);
/* Global list of callbacks and associated lock. */
static struct rcu_head *rcu_tasks_cbs_head;
static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
/* Track exiting tasks in order to allow them to be waited for. */
@ -378,13 +379,17 @@ module_param(rcu_task_stall_timeout, int, 0644);
void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp))
{
unsigned long flags;
bool needwake;
rhp->next = NULL;
rhp->func = func;
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
needwake = !rcu_tasks_cbs_head;
*rcu_tasks_cbs_tail = rhp;
rcu_tasks_cbs_tail = &rhp->next;
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
if (needwake)
wake_up(&rcu_tasks_cbs_wq);
}
EXPORT_SYMBOL_GPL(call_rcu_tasks);
@ -495,8 +500,12 @@ static int __noreturn rcu_tasks_kthread(void *arg)
/* If there were none, wait a bit and start over. */
if (!list) {
schedule_timeout_interruptible(HZ);
WARN_ON(signal_pending(current));
wait_event_interruptible(rcu_tasks_cbs_wq,
rcu_tasks_cbs_head);
if (!rcu_tasks_cbs_head) {
WARN_ON(signal_pending(current));
schedule_timeout_interruptible(HZ/10);
}
continue;
}
@ -602,6 +611,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
list = next;
cond_resched();
}
schedule_timeout_uninterruptible(HZ/10);
}
}