Commit-ID: c7b24d2b9a0f2ce19fdf631d3148c80a8f6010b1
Gitweb: http://git.kernel.org/tip/c7b24d2b9a0f2ce19fdf631d3148c80a8f6010b1
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 28 Jul 2014 14:39:25 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Sun, 7 Sep 2014 16:27:27 -0700
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: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/update.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index bad7dbd..444c8a3 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -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);
}
}
--
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