From 511885d7061eda3eb1faf3f57dcc936ff75863f1 Mon Sep 17 00:00:00 2001
From: Davidlohr Bueso <dave@stgolabs.net>
Date: Wed, 24 Jul 2019 08:23:23 -0700
Subject: 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.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190724152323.bojciei3muvfxalm@linux-r8p5
---
lib/timerqueue.c | 30 ++++++++++++------------------
1 file changed, 12 insertions(+), 18 deletions(-)
(limited to 'lib/timerqueue.c')
diff --git a/lib/timerqueue.c b/lib/timerqueue.c
index bc7e64df27df..c52710964593 100644
--- a/lib/timerqueue.c
+++ b/lib/timerqueue.c
@@ -26,9 +26,10 @@
*/
bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
{
- struct rb_node **p = &head->head.rb_node;
+ struct rb_node **p = &head->rb_root.rb_root.rb_node;
struct rb_node *parent = NULL;
- struct timerqueue_node *ptr;
+ struct timerqueue_node *ptr;
+ bool leftmost = true;
/* Make sure we don't add nodes that are already added */
WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
@@ -36,19 +37,17 @@ bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
while (*p) {
parent = *p;
ptr = rb_entry(parent, struct timerqueue_node, node);
- if (node->expires < ptr->expires)
+ if (node->expires < ptr->expires) {
p = &(*p)->rb_left;
- else
+ } else {
p = &(*p)->rb_right;
+ leftmost = false;
+ }
}
rb_link_node(&node->node, parent, p);
- rb_insert_color(&node->node, &head->head);
+ rb_insert_color_cached(&node->node, &head->rb_root, leftmost);
- if (!head->next || node->expires < head->next->expires) {
- head->next = node;
- return true;
- }
- return false;
+ return leftmost;
}
EXPORT_SYMBOL_GPL(timerqueue_add);
@@ -65,15 +64,10 @@ bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
{
WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
- /* update next pointer */
- if (head->next == node) {
- struct rb_node *rbn = rb_next(&node->node);
-
- head->next = rb_entry_safe(rbn, struct timerqueue_node, node);
- }
- rb_erase(&node->node, &head->head);
+ rb_erase_cached(&node->node, &head->rb_root);
RB_CLEAR_NODE(&node->node);
- return head->next != NULL;
+
+ return !RB_EMPTY_ROOT(&head->rb_root.rb_root);
}
EXPORT_SYMBOL_GPL(timerqueue_del);
--
cgit v1.2.3