linux/lib/timerqueue.c
Davidlohr Bueso 511885d706 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
2019-07-24 17:38:01 +02:00

95 lines
2.5 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Generic Timer-queue
*
* Manages a simple queue of timers, ordered by expiration time.
* Uses rbtrees for quick list adds and expiration.
*
* NOTE: All of the following functions need to be serialized
* to avoid races. No locking is done by this library code.
*/
#include <linux/bug.h>
#include <linux/timerqueue.h>
#include <linux/rbtree.h>
#include <linux/export.h>
/**
* timerqueue_add - Adds timer to timerqueue.
*
* @head: head of timerqueue
* @node: timer node to be added
*
* Adds the timer node to the timerqueue, sorted by the node's expires
* value. Returns true if the newly added timer is the first expiring timer in
* the queue.
*/
bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
{
struct rb_node **p = &head->rb_root.rb_root.rb_node;
struct rb_node *parent = NULL;
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));
while (*p) {
parent = *p;
ptr = rb_entry(parent, struct timerqueue_node, node);
if (node->expires < ptr->expires) {
p = &(*p)->rb_left;
} else {
p = &(*p)->rb_right;
leftmost = false;
}
}
rb_link_node(&node->node, parent, p);
rb_insert_color_cached(&node->node, &head->rb_root, leftmost);
return leftmost;
}
EXPORT_SYMBOL_GPL(timerqueue_add);
/**
* timerqueue_del - Removes a timer from the timerqueue.
*
* @head: head of timerqueue
* @node: timer node to be removed
*
* Removes the timer node from the timerqueue. Returns true if the queue is
* not empty after the remove.
*/
bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
{
WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
rb_erase_cached(&node->node, &head->rb_root);
RB_CLEAR_NODE(&node->node);
return !RB_EMPTY_ROOT(&head->rb_root.rb_root);
}
EXPORT_SYMBOL_GPL(timerqueue_del);
/**
* timerqueue_iterate_next - Returns the timer after the provided timer
*
* @node: Pointer to a timer.
*
* Provides the timer that is after the given node. This is used, when
* necessary, to iterate through the list of timers in a timer list
* without modifying the list.
*/
struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
{
struct rb_node *next;
if (!node)
return NULL;
next = rb_next(&node->node);
if (!next)
return NULL;
return container_of(next, struct timerqueue_node, node);
}
EXPORT_SYMBOL_GPL(timerqueue_iterate_next);