linux-kernel - [RFC][PATCH 2/7] PM / Sleep: Use wait queue to signal "no wakeup events in progress"

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Message-Id: <201202220033.25523.rjw@sisk.pl>
Date:	Wed, 22 Feb 2012 00:33:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>, markgross@...gnar.org,
	Matthew Garrett <mjg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	Alan Stern <stern@...land.harvard.edu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: [RFC][PATCH 2/7] PM / Sleep: Use wait queue to signal "no wakeup events in progress"

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 |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 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_prepare - Prepare a new wakeup source for initialization.
  * @ws: Wakeup source to prepare.
@@ -442,6 +442,7 @@ 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;
 
@@ -476,6 +477,10 @@ 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 && waitqueue_active(&wakeup_count_wait_queue))
+		wake_up(&wakeup_count_wait_queue);
 }
 
 /**
@@ -667,14 +672,19 @@ 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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