lkml.org 
[lkml]   [2014]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v5 tip/core/rcu 09/16] rcu: Improve RCU-tasks energy efficiency
On Mon, Aug 11, 2014 at 6:48 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
>
> 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>
> ---
> 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 f1535404a79e..1256a900cd01 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -368,6 +368,7 @@ 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. */
> @@ -381,13 +382,17 @@ 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);

I think you want

needwake = !!rcu_tasks_cbs_head;

otherwise it will wake up when rcu_tasks_cbs_head is null, no?

>
> @@ -498,8 +503,12 @@ 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;
> }
>
> @@ -605,6 +614,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
> list = next;
> cond_resched();
> }
> + schedule_timeout_uninterruptible(HZ/10);
> }
> }
>
> --
> 1.8.1.5
>



--
Pranith


\
 
 \ /
  Last update: 2014-08-15 00:01    [W:0.175 / U:0.424 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site