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https://github.com/torvalds/linux
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511885d706
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
94 lines
2.5 KiB
C
94 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Generic Timer-queue
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*
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* Manages a simple queue of timers, ordered by expiration time.
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* Uses rbtrees for quick list adds and expiration.
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*
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* NOTE: All of the following functions need to be serialized
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* to avoid races. No locking is done by this library code.
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*/
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#include <linux/bug.h>
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#include <linux/timerqueue.h>
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#include <linux/rbtree.h>
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#include <linux/export.h>
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/**
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* timerqueue_add - Adds timer to timerqueue.
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*
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* @head: head of timerqueue
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* @node: timer node to be added
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*
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* Adds the timer node to the timerqueue, sorted by the node's expires
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* value. Returns true if the newly added timer is the first expiring timer in
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* the queue.
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*/
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bool timerqueue_add(struct timerqueue_head *head, struct timerqueue_node *node)
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{
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struct rb_node **p = &head->rb_root.rb_root.rb_node;
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struct rb_node *parent = NULL;
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struct timerqueue_node *ptr;
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bool leftmost = true;
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/* Make sure we don't add nodes that are already added */
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WARN_ON_ONCE(!RB_EMPTY_NODE(&node->node));
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while (*p) {
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parent = *p;
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ptr = rb_entry(parent, struct timerqueue_node, node);
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if (node->expires < ptr->expires) {
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p = &(*p)->rb_left;
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} else {
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p = &(*p)->rb_right;
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leftmost = false;
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}
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}
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rb_link_node(&node->node, parent, p);
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rb_insert_color_cached(&node->node, &head->rb_root, leftmost);
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return leftmost;
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}
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EXPORT_SYMBOL_GPL(timerqueue_add);
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/**
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* timerqueue_del - Removes a timer from the timerqueue.
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*
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* @head: head of timerqueue
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* @node: timer node to be removed
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*
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* Removes the timer node from the timerqueue. Returns true if the queue is
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* not empty after the remove.
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*/
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bool timerqueue_del(struct timerqueue_head *head, struct timerqueue_node *node)
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{
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WARN_ON_ONCE(RB_EMPTY_NODE(&node->node));
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rb_erase_cached(&node->node, &head->rb_root);
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RB_CLEAR_NODE(&node->node);
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return !RB_EMPTY_ROOT(&head->rb_root.rb_root);
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}
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EXPORT_SYMBOL_GPL(timerqueue_del);
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/**
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* timerqueue_iterate_next - Returns the timer after the provided timer
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*
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* @node: Pointer to a timer.
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*
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* Provides the timer that is after the given node. This is used, when
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* necessary, to iterate through the list of timers in a timer list
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* without modifying the list.
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*/
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struct timerqueue_node *timerqueue_iterate_next(struct timerqueue_node *node)
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{
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struct rb_node *next;
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if (!node)
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return NULL;
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next = rb_next(&node->node);
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if (!next)
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return NULL;
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return container_of(next, struct timerqueue_node, node);
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}
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EXPORT_SYMBOL_GPL(timerqueue_iterate_next);
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