lib/timerqueue: Rely on rbtree semantics for next timer

Simplify the timerqueue code by using cached rbtrees and rely on the tree leftmost node semantics to get the timer with earliest expiration time. This is a drop in conversion, and therefore semantics remain untouched. The runtime overhead of cached rbtrees is be pretty much the same as the current head->next method, noting that when removing the leftmost node, a common operation for the timerqueue, the rb_next(leftmost) is O(1) as well, so the next timer will either be the right node or its parent. Therefore no extra pointer chasing. Finally, the size of the struct timerqueue_head remains the same. Passes several hours of rcutorture.

Davidlohr Bueso committed 7 years ago

Commit 511885d1 parent ad5e4272 files · +18 −25Browse files

Showing the changes to include/linux/timerqueue.h (1 of 2 files). Show all

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include/linux/timerqueue.h+6−7

@@ -12,8 +12,7 @@ struct timerqueue_node { · 11 unmodified lines
12	12	};
13	13
14	14	struct timerqueue_head {
15		− struct rb_root head;
16		− struct timerqueue_node *next;
	15	+ struct rb_root_cached rb_root;
17	16	};
18	17
19	18
@@ -29,13 +28,14 @@ extern struct timerqueue_node *timerqueue_iterate_next( · 9 unmodified lines
29	28	*
30	29	* @head: head of timerqueue
31	30	*
32		− * Returns a pointer to the timer node that has the
33		− * earliest expiration time.
	31	+ * Returns a pointer to the timer node that has the earliest expiration time.
34	32	*/
35	33	static inline
36	34	struct timerqueue_node timerqueue_getnext(struct timerqueue_head head)
37	35	{
38		− return head->next;
	36	+ struct rb_node *leftmost = rb_first_cached(&head->rb_root);
	37	+
	38	+ return rb_entry(leftmost, struct timerqueue_node, node);
39	39	}
40	40
41	41	static inline void timerqueue_init(struct timerqueue_node *node)
@@ -45,7 +45,6 @@ static inline void timerqueue_init(struct timerqueue_node *node) · 3 unmodified lines
45	45
46	46	static inline void timerqueue_init_head(struct timerqueue_head *head)
47	47	{
48		− head->head = RB_ROOT;
49		− head->next = NULL;
	48	+ head->rb_root = RB_ROOT_CACHED;
50	49	}
51	50	#endif /* _LINUX_TIMERQUEUE_H */

lib/timerqueue: Rely on rbtree semantics for next timer

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