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Commit c7b24d2b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Improve RCU-tasks energy efficiency 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 52db30ab

kernel/rcu/update.c

+12 −2
Original line number Diff line number Diff line
@@ -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);

			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);

	}

}