[hrtimer] Remove listhead from hrtimer struct

The list_head in the hrtimer structure was introduced for easy access to the first timer with the further extensions of real high resolution timers in mind, but it turned out in the course of development that it is not necessary for the standard use case. Remove the list head and access the first expiry timer by a datafield in the timer base. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

[hrtimer] Remove listhead from hrtimer struct
The list_head in the hrtimer structure was introduced for easy access to the first timer with the further extensions of real high resolution timers in mind, but it turned out in the course of development that it is not necessary for the standard use case. Remove the list head and access the first expiry timer by a datafield in the timer base. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Thomas Gleixner
1 parent 593195f9b2
Showing 2 changed files with 16 additions and 17 deletions Side-by-side Diff
include/linux/hrtimer.h
kernel/hrtimer.c
@@ -49,8 +49,6 @@
  * struct hrtimer - the basic hrtimer structure
  *
  * @node:	red black tree node for time ordered insertion
- * @list:	list head for easier access to the time ordered list,
- *		without walking the red black tree.
  * @expires:	the absolute expiry time in the hrtimers internal
  *		representation. The time is related to the clock on
  *		which the timer is based.
@@ -63,7 +61,6 @@
  */
 struct hrtimer {
 	struct rb_node		node;
-	struct list_head	list;
 	ktime_t			expires;
 	enum hrtimer_state	state;
 	int			(*function)(void *);
@@ -78,7 +75,7 @@
  *		to a base on another cpu.
  * @lock:	lock protecting the base and associated timers
  * @active:	red black tree root node for the active timers
- * @pending:	list of pending timers for simple time ordered access
+ * @first:	pointer to the timer node which expires first
  * @resolution:	the resolution of the clock, in nanoseconds
  * @get_time:	function to retrieve the current time of the clock
  * @curr_timer:	the timer which is executing a callback right now
@@ -87,7 +84,7 @@
 	clockid_t		index;
 	spinlock_t		lock;
 	struct rb_root		active;
-	struct list_head	pending;
+	struct rb_node		*first;
 	unsigned long		resolution;
 	ktime_t			(*get_time)(void);
 	struct hrtimer		*curr_timer;
@@ -314,7 +314,6 @@
 static void enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
 {
 	struct rb_node **link = &base->active.rb_node;
-	struct list_head *prev = &base->pending;
 	struct rb_node *parent = NULL;
 	struct hrtimer *entry;
  
  
  
  
  
  
@@ -330,23 +329,24 @@
 		 */
 		if (timer->expires.tv64 < entry->expires.tv64)
 			link = &(*link)->rb_left;
-		else {
+		else
 			link = &(*link)->rb_right;
-			prev = &entry->list;
-		}
 	}
  
 	/*
-	 * Insert the timer to the rbtree and to the sorted list:
+	 * Insert the timer to the rbtree and check whether it
+	 * replaces the first pending timer
 	 */
 	rb_link_node(&timer->node, parent, link);
 	rb_insert_color(&timer->node, &base->active);
-	list_add(&timer->list, prev);
  
 	timer->state = HRTIMER_PENDING;
+
+	if (!base->first || timer->expires.tv64 <
+	    rb_entry(base->first, struct hrtimer, node)->expires.tv64)
+		base->first = &timer->node;
 }
  
-
 /*
  * __remove_hrtimer - internal function to remove a timer
  *
  
@@ -355,9 +355,11 @@
 static void __remove_hrtimer(struct hrtimer *timer, struct hrtimer_base *base)
 {
 	/*
-	 * Remove the timer from the sorted list and from the rbtree:
+	 * Remove the timer from the rbtree and replace the
+	 * first entry pointer if necessary.
 	 */
-	list_del(&timer->list);
+	if (base->first == &timer->node)
+		base->first = rb_next(&timer->node);
 	rb_erase(&timer->node, &base->active);
 }
  
  
  
@@ -529,16 +531,17 @@
 static inline void run_hrtimer_queue(struct hrtimer_base *base)
 {
 	ktime_t now = base->get_time();
+	struct rb_node *node;
  
 	spin_lock_irq(&base->lock);
  
-	while (!list_empty(&base->pending)) {
+	while ((node = base->first)) {
 		struct hrtimer *timer;
 		int (*fn)(void *);
 		int restart;
 		void *data;
  
-		timer = list_entry(base->pending.next, struct hrtimer, list);
+		timer = rb_entry(node, struct hrtimer, node);
 		if (now.tv64 <= timer->expires.tv64)
 			break;
  
@@ -732,7 +735,6 @@
  
 	for (i = 0; i < MAX_HRTIMER_BASES; i++) {
 		spin_lock_init(&base->lock);
-		INIT_LIST_HEAD(&base->pending);
 		base++;
 	}
 }
...	...	@@ -49,8 +49,6 @@
49	49	* struct hrtimer - the basic hrtimer structure
50	50	*
51	51	* @node: red black tree node for time ordered insertion
52		- * @list: list head for easier access to the time ordered list,
53		- * without walking the red black tree.
54	52	* @expires: the absolute expiry time in the hrtimers internal
55	53	* representation. The time is related to the clock on
56	54	* which the timer is based.
...	...	@@ -63,7 +61,6 @@
63	61	*/
64	62	struct hrtimer {
65	63	struct rb_node node;
66		- struct list_head list;
67	64	ktime_t expires;
68	65	enum hrtimer_state state;
69	66	int (function)(void );
...	...	@@ -78,7 +75,7 @@
78	75	* to a base on another cpu.
79	76	* @lock: lock protecting the base and associated timers
80	77	* @active: red black tree root node for the active timers
81		- * @pending: list of pending timers for simple time ordered access
	78	+ * @first: pointer to the timer node which expires first
82	79	* @resolution: the resolution of the clock, in nanoseconds
83	80	* @get_time: function to retrieve the current time of the clock
84	81	* @curr_timer: the timer which is executing a callback right now
...	...	@@ -87,7 +84,7 @@
87	84	clockid_t index;
88	85	spinlock_t lock;
89	86	struct rb_root active;
90		- struct list_head pending;
	87	+ struct rb_node *first;
91	88	unsigned long resolution;
92	89	ktime_t (*get_time)(void);
93	90	struct hrtimer *curr_timer;
...	...	@@ -314,7 +314,6 @@
314	314	static void enqueue_hrtimer(struct hrtimer timer, struct hrtimer_base base)
315	315	{
316	316	struct rb_node **link = &base->active.rb_node;
317		- struct list_head *prev = &base->pending;
318	317	struct rb_node *parent = NULL;
319	318	struct hrtimer *entry;
320	319
321	320
322	321
323	322
324	323
325	324
...	...	@@ -330,23 +329,24 @@
330	329	*/
331	330	if (timer->expires.tv64 < entry->expires.tv64)
332	331	link = &(*link)->rb_left;
333		- else {
	332	+ else
334	333	link = &(*link)->rb_right;
335		- prev = &entry->list;
336		- }
337	334	}
338	335
339	336	/*
340		- * Insert the timer to the rbtree and to the sorted list:
	337	+ * Insert the timer to the rbtree and check whether it
	338	+ * replaces the first pending timer
341	339	*/
342	340	rb_link_node(&timer->node, parent, link);
343	341	rb_insert_color(&timer->node, &base->active);
344		- list_add(&timer->list, prev);
345	342
346	343	timer->state = HRTIMER_PENDING;
	344	+
	345	+ if (!base->first \|\| timer->expires.tv64 <
	346	+ rb_entry(base->first, struct hrtimer, node)->expires.tv64)
	347	+ base->first = &timer->node;
347	348	}
348	349
349		-
350	350	/*
351	351	* __remove_hrtimer - internal function to remove a timer
352	352	*
353	353
...	...	@@ -355,9 +355,11 @@
355	355	static void __remove_hrtimer(struct hrtimer timer, struct hrtimer_base base)
356	356	{
357	357	/*
358		- * Remove the timer from the sorted list and from the rbtree:
	358	+ * Remove the timer from the rbtree and replace the
	359	+ * first entry pointer if necessary.
359	360	*/
360		- list_del(&timer->list);
	361	+ if (base->first == &timer->node)
	362	+ base->first = rb_next(&timer->node);
361	363	rb_erase(&timer->node, &base->active);
362	364	}
363	365
364	366
365	367
...	...	@@ -529,16 +531,17 @@
529	531	static inline void run_hrtimer_queue(struct hrtimer_base *base)
530	532	{
531	533	ktime_t now = base->get_time();
	534	+ struct rb_node *node;
532	535
533	536	spin_lock_irq(&base->lock);
534	537
535		- while (!list_empty(&base->pending)) {
	538	+ while ((node = base->first)) {
536	539	struct hrtimer *timer;
537	540	int (fn)(void );
538	541	int restart;
539	542	void *data;
540	543
541		- timer = list_entry(base->pending.next, struct hrtimer, list);
	544	+ timer = rb_entry(node, struct hrtimer, node);
542	545	if (now.tv64 <= timer->expires.tv64)
543	546	break;
544	547
...	...	@@ -732,7 +735,6 @@
732	735
733	736	for (i = 0; i < MAX_HRTIMER_BASES; i++) {
734	737	spin_lock_init(&base->lock);
735		- INIT_LIST_HEAD(&base->pending);
736	738	base++;
737	739	}
738	740	}