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timer: add scalable RB-tree based timer infrastructure 

This patch adds RB-tree based timers which scales better than the
previous list-based implementation.

It does not require any API changes. It breaks ABI because the
osmo_timer_list structure has changed though (to avoid this in
the future, we can put internal data in some private structure).

The following table summarizes the worst-case computational complexity
of this new implementation versus the previous one:

                                rb-tree         list-based
                                -------         ----------
calculate next timer to expire  O(1)            O(n)
insertion of new timer          O(log n)        O(n)
deletion of timer               O(log n)        O(1)
timer-fired scheduler           O(log n)        O(3n)

The most repeated cases are:

* the calculation of the next timer to expire, that happens in every
  loop of our select function.

* the timer-fired scheduler execution.

This new implementation only loses in the deletion of timer scenario,
this happens because we may need to rebalance the tree after the
removal.

So I think there is some real gain if we have some situation in which
we have to handle lots of timers.
This commit is contained in:
Pablo Neira Ayuso 2011-09-26 11:45:03 +02:00 committed by Harald Welte
parent f74db0b33d
commit 066c912fd3
2 changed files with 98 additions and 84 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/osmocom/core/timer.h
View File

@ -32,6 +32,7 @@
#include <sys/time.h>
#include <osmocom/core/linuxlist.h>
#include <osmocom/core/linuxrbtree.h>
/**
* Timer management:
@ -51,11 +52,10 @@
*/
/*! \brief A structure representing a single instance of a timer */
struct osmo_timer_list {
struct llist_head entry; /*!< \brief linked list header */
struct rb_node node; /*!< \brief rb-tree node header */
struct llist_head list; /*!< \brief internal list header */
struct timeval timeout; /*!< \brief expiration time */
unsigned int active : 1; /*!< \brief is it active? */
unsigned int handled : 1; /*!< \brief did we already handle it */
unsigned int in_list : 1; /*!< \brief is it in the global list? */
void (*cb)(void*); /*!< \brief call-back called at timeout */
void *data; /*!< \brief user data for callback */

176
src/timer.c
View File

@ -1,7 +1,12 @@
/*
* (C) 2008,2009 by Holger Hans Peter Freyther <zecke@selfish.org>
* (C) 2011 by Harald Welte <laforge@gnumonks.org>
* All Rights Reserved
*
* Authors: Holger Hans Peter Freyther <zecke@selfish.org>
* Harald Welte <laforge@gnumonks.org>
* Pablo Neira Ayuso <pablo@gnumonks.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
@ -18,6 +23,10 @@
*
*/
/* These store the amount of time that we wait until next timer expires. */
static struct timeval nearest;
static struct timeval *nearest_p;
/*! \addtogroup timer
* @{
*/
@ -27,35 +36,41 @@
#include <assert.h>
#include <string.h>
#include <limits.h>
#include <osmocom/core/timer.h>
#include <osmocom/core/linuxlist.h>
static LLIST_HEAD(timer_list);
static struct timeval s_nearest_time;
static struct timeval s_select_time;
static struct rb_root timer_root = RB_ROOT;
#define MICRO_SECONDS 1000000LL
static void __add_timer(struct osmo_timer_list *timer)
{
struct rb_node **new = &(timer_root.rb_node);
struct rb_node *parent = NULL;
#define TIME_SMALLER(left, right) \
(left.tv_sec*MICRO_SECONDS+left.tv_usec) <= (right.tv_sec*MICRO_SECONDS+right.tv_usec)
while (*new) {
struct osmo_timer_list *this;
this = container_of(*new, struct osmo_timer_list, node);
parent = *new;
if (timercmp(&timer->timeout, &this->timeout, <))
new = &((*new)->rb_left);
else
new = &((*new)->rb_right);
}
rb_link_node(&timer->node, parent, new);
rb_insert_color(&timer->node, &timer_root);
}
/*! \brief add a new timer to the timer management
* \param[in] timer the timer that should be added
*/
void osmo_timer_add(struct osmo_timer_list *timer)
{
struct osmo_timer_list *list_timer;
/* TODO: Optimize and remember the closest item... */
timer->active = 1;
/* this might be called from within update_timers */
llist_for_each_entry(list_timer, &timer_list, entry)
if (timer == list_timer)
return;
timer->in_list = 1;
llist_add(&timer->entry, &timer_list);
INIT_LLIST_HEAD(&timer->list);
__add_timer(timer);
}
/*! \brief schedule a timer at a given future relative time
@ -74,10 +89,9 @@ osmo_timer_schedule(struct osmo_timer_list *timer, int seconds, int microseconds
struct timeval current_time;
gettimeofday(&current_time, NULL);
unsigned long long currentTime = current_time.tv_sec * MICRO_SECONDS + current_time.tv_usec;
currentTime += seconds * MICRO_SECONDS + microseconds;
timer->timeout.tv_sec = currentTime / MICRO_SECONDS;
timer->timeout.tv_usec = currentTime % MICRO_SECONDS;
timer->timeout.tv_sec = seconds;
timer->timeout.tv_usec = microseconds;
timeradd(&timer->timeout, &current_time, &timer->timeout);
osmo_timer_add(timer);
}
@ -89,10 +103,12 @@ osmo_timer_schedule(struct osmo_timer_list *timer, int seconds, int microseconds
*/
void osmo_timer_del(struct osmo_timer_list *timer)
{
if (timer->in_list) {
if (timer->active) {
timer->active = 0;
timer->in_list = 0;
llist_del(&timer->entry);
rb_erase(&timer->node, &timer_root);
/* make sure this is not already scheduled for removal. */
if (!llist_empty(&timer->list))
llist_del_init(&timer->list);
}
}
@ -116,26 +132,28 @@ int osmo_timer_pending(struct osmo_timer_list *timer)
*/
struct timeval *osmo_timers_nearest(void)
{
struct timeval current_time;
static struct timeval no_timers = { 0, 0 };
if (s_nearest_time.tv_sec == 0 && s_nearest_time.tv_usec == 0)
return NULL;
if (nearest_p != NULL && !timerisset(nearest_p))
return nearest_p;
else
return &no_timers;
}
if (gettimeofday(&current_time, NULL) == -1)
return NULL;
unsigned long long nearestTime = s_nearest_time.tv_sec * MICRO_SECONDS + s_nearest_time.tv_usec;
unsigned long long currentTime = current_time.tv_sec * MICRO_SECONDS + current_time.tv_usec;
if (nearestTime < currentTime) {
s_select_time.tv_sec = 0;
s_select_time.tv_usec = 0;
static void update_nearest(struct timeval *cand, struct timeval *current)
{
if (cand->tv_sec != LONG_MAX) {
if (timercmp(cand, current, >))
timersub(cand, current, &nearest);
else {
/* loop again inmediately */
nearest.tv_sec = 0;
nearest.tv_usec = 0;
}
nearest_p = &nearest;
} else {
s_select_time.tv_sec = (nearestTime - currentTime) / MICRO_SECONDS;
s_select_time.tv_usec = (nearestTime - currentTime) % MICRO_SECONDS;
nearest_p = NULL;
}
return &s_select_time;
}
/*
@ -143,17 +161,18 @@ struct timeval *osmo_timers_nearest(void)
*/
void osmo_timers_prepare(void)
{
struct osmo_timer_list *timer, *nearest_timer = NULL;
llist_for_each_entry(timer, &timer_list, entry) {
if (!nearest_timer || TIME_SMALLER(timer->timeout, nearest_timer->timeout)) {
nearest_timer = timer;
}
}
struct rb_node *node;
struct timeval current;
if (nearest_timer) {
s_nearest_time = nearest_timer->timeout;
gettimeofday(&current, NULL);
node = rb_first(&timer_root);
if (node) {
struct osmo_timer_list *this;
this = container_of(node, struct osmo_timer_list, node);
update_nearest(&this->timeout, &current);
} else {
memset(&s_nearest_time, 0, sizeof(struct timeval));
nearest_p = NULL;
}
}
@ -163,46 +182,41 @@ void osmo_timers_prepare(void)
int osmo_timers_update(void)
{
struct timeval current_time;
struct osmo_timer_list *timer, *tmp;
struct rb_node *node;
struct llist_head timer_eviction_list;
struct osmo_timer_list *this;
int work = 0;
gettimeofday(&current_time, NULL);
INIT_LLIST_HEAD(&timer_eviction_list);
for (node = rb_first(&timer_root); node; node = rb_next(node)) {
this = container_of(node, struct osmo_timer_list, node);
if (timercmp(&this->timeout, &current_time, >))
break;
llist_add(&this->list, &timer_eviction_list);
}
/*
* The callbacks might mess with our list and in this case
* even llist_for_each_entry_safe is not safe to use. To allow
* del_timer, add_timer, schedule_timer to be called from within
* the callback we jump through some loops.
* osmo_timer_del to be called from within the callback we need
* to restart the iteration for each element scheduled for removal.
*
* First we set the handled flag of each active timer to zero,
* then we iterate over the list and execute the callbacks. As the
* list might have been changed (specially the next) from within
* the callback we have to start over again. Once every callback
* is dispatched we will remove the non-active from the list.
*
* TODO: If this is a performance issue we can poison a global
* variable in add_timer and del_timer and only then restart.
* The problematic scenario is the following: Given two timers A
* and B that have expired at the same time. Thus, they are both
* in the eviction list in this order: A, then B. If we remove
* timer B from the A's callback, we continue with B in the next
* iteration step, leading to an access-after-release.
*/
llist_for_each_entry(timer, &timer_list, entry) {
timer->handled = 0;
}
restart:
llist_for_each_entry(timer, &timer_list, entry) {
if (!timer->handled && TIME_SMALLER(timer->timeout, current_time)) {
timer->handled = 1;
timer->active = 0;
(*timer->cb)(timer->data);
work = 1;
goto restart;
}
}
llist_for_each_entry_safe(timer, tmp, &timer_list, entry) {
timer->handled = 0;
if (!timer->active) {
osmo_timer_del(timer);
}
llist_for_each_entry(this, &timer_eviction_list, list) {
osmo_timer_del(this);
this->cb(this->data);
work = 1;
goto restart;
}
return work;
@ -210,10 +224,10 @@ restart:
int osmo_timers_check(void)
{
struct osmo_timer_list *timer;
struct rb_node *node;
int i = 0;
llist_for_each_entry(timer, &timer_list, entry) {
for (node = rb_first(&timer_root); node; node = rb_next(node)) {
i++;
}
return i;