linux-kernel - Re: [PATCH 4/8] PM / Sleep: Use wait queue to signal "no wakeup events in progress"

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Date:	Thu, 9 Feb 2012 10:10:54 +1100
From:	NeilBrown <neilb@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>, markgross@...gnar.org,
	Matthew Garrett <mjg@...hat.com>,
	Greg KH <greg@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Brian Swetland <swetland@...gle.com>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 4/8] PM / Sleep: Use wait queue to signal "no wakeup
 events in progress"

On Tue, 7 Feb 2012 02:04:19 +0100 "Rafael J. Wysocki" <rjw@...k.pl> wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> The current wakeup source deactivation code doesn't do anything when
> the counter of wakeup events in progress goes down to zero, which
> requires pm_get_wakeup_count() to poll that counter periodically.
> Although this reduces the average time it takes to deactivate a
> wakeup source, it also may lead to a substantial amount of unnecessary
> polling if there are extended periods of wakeup activity.  Thus it
> seems reasonable to use a wait queue for signaling the "no wakeup
> events in progress" condition and remove the polling.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---
>  drivers/base/power/wakeup.c |   18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> Index: linux/drivers/base/power/wakeup.c
> ===================================================================
> --- linux.orig/drivers/base/power/wakeup.c
> +++ linux/drivers/base/power/wakeup.c
> @@ -17,8 +17,6 @@
>  
>  #include "power.h"
>  
> -#define TIMEOUT		100
> -
>  /*
>   * If set, the suspend/hibernate code will abort transitions to a sleep state
>   * if wakeup events are registered during or immediately before the transition.
> @@ -52,6 +50,8 @@ static void pm_wakeup_timer_fn(unsigned
>  
>  static LIST_HEAD(wakeup_sources);
>  
> +static DECLARE_WAIT_QUEUE_HEAD(wakeup_count_wait_queue);
> +
>  /**
>   * wakeup_source_create - Create a struct wakeup_source object.
>   * @name: Name of the new wakeup source.
> @@ -84,7 +84,7 @@ void wakeup_source_destroy(struct wakeup
>  	while (ws->active) {
>  		spin_unlock_irq(&ws->lock);
>  
> -		schedule_timeout_interruptible(msecs_to_jiffies(TIMEOUT));
> +		schedule_timeout_interruptible(msecs_to_jiffies(100));
>  
>  		spin_lock_irq(&ws->lock);
>  	}
> @@ -411,6 +411,7 @@ EXPORT_SYMBOL_GPL(pm_stay_awake);
>   */
>  static void wakeup_source_deactivate(struct wakeup_source *ws)
>  {
> +	unsigned int cnt, inpr;
>  	ktime_t duration;
>  	ktime_t now;
>  
> @@ -444,6 +445,10 @@ static void wakeup_source_deactivate(str
>  	 * couter of wakeup events in progress simultaneously.
>  	 */
>  	atomic_add(MAX_IN_PROGRESS, &combined_event_count);
> +
> +	split_counters(&cnt, &inpr);
> +	if (!inpr)
> +		wake_up_all(&wakeup_count_wait_queue);
>  }

Would it be worth making this:

     if (!inpr && waitqueue_active(&wakeup_count_wait_queue))
		wake_up_all(&wakeup_count_wait_queue);

??
It would often save a spinlock.

Also was there a reason you used wake_up_all().  That is only really needed
were EXCLUSIVE waits are happening, and there aren't any of those.

Thanks,
NeilBrown


>  
>  /**
> @@ -624,14 +629,19 @@ bool pm_wakeup_pending(void)
>  bool pm_get_wakeup_count(unsigned int *count)
>  {
>  	unsigned int cnt, inpr;
> +	DEFINE_WAIT(wait);
>  
>  	for (;;) {
> +		prepare_to_wait(&wakeup_count_wait_queue, &wait,
> +				TASK_INTERRUPTIBLE);
>  		split_counters(&cnt, &inpr);
>  		if (inpr == 0 || signal_pending(current))
>  			break;
>  		pm_wakeup_update_hit_counts();
> -		schedule_timeout_interruptible(msecs_to_jiffies(TIMEOUT));
> +
> +		schedule();
>  	}
> +	finish_wait(&wakeup_count_wait_queue, &wait);
>  
>  	split_counters(&cnt, &inpr);
>  	*count = cnt;


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