26 Sep
2011
26 Sep
'11
1:35 p.m.
From: Pablo Neira Ayuso <pablo(a)gnumonks.org>
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.
---
include/osmocom/core/timer.h | 6 +-
src/timer.c | 176 +++++++++++++++++++++++-------------------
2 files changed, 98 insertions(+), 84 deletions(-)
diff --git a/include/osmocom/core/timer.h b/include/osmocom/core/timer.h
index 8f8c826..30f558b 100644
--- a/include/osmocom/core/timer.h
+++ b/include/osmocom/core/timer.h
@@ -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 */
diff --git a/src/timer.c b/src/timer.c
index ed2b296..6852983 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -1,7 +1,12 @@
/*
* (C) 2008,2009 by Holger Hans Peter Freyther <zecke(a)selfish.org>
+ * (C) 2011 by Harald Welte <laforge(a)gnumonks.org>
* All Rights Reserved
*
+ * Authors: Holger Hans Peter Freyther <zecke(a)selfish.org>
+ * Harald Welte <laforge(a)gnumonks.org>
+ * Pablo Neira Ayuso <pablo(a)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 struct rb_root timer_root = RB_ROOT;
+
+static void __add_timer(struct osmo_timer_list *timer)
+{
+ struct rb_node **new = &(timer_root.rb_node);
+ struct rb_node *parent = NULL;
-static LLIST_HEAD(timer_list);
-static struct timeval s_nearest_time;
-static struct timeval s_select_time;
+ while (*new) {
+ struct osmo_timer_list *this;
-#define MICRO_SECONDS 1000000LL
+ this = container_of(*new, struct osmo_timer_list, node);
-#define TIME_SMALLER(left, right) \
- (left.tv_sec*MICRO_SECONDS+left.tv_usec) <=
(right.tv_sec*MICRO_SECONDS+right.tv_usec)
+ 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(¤t_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, ¤t_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;
-
- if (s_nearest_time.tv_sec == 0 && s_nearest_time.tv_usec == 0)
- return NULL;
-
- if (gettimeofday(¤t_time, NULL) == -1)
- return NULL;
+ static struct timeval no_timers = { 0, 0 };
- 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 (nearest_p != NULL && !timerisset(nearest_p))
+ return nearest_p;
+ else
+ return &no_timers;
+}
- 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;
+
+ gettimeofday(¤t, NULL);
- if (nearest_timer) {
- s_nearest_time = nearest_timer->timeout;
+ 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, ¤t);
} 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(¤t_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, ¤t_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;
--
1.7.2.5