Introduce mod_timer_noact() which for example is to replace the calls to
del_timer()/add_timer() in __nf_ct_refresh_acct(). It works like mod_timer()
but doesn't activate or modify the timeout of an inactive timer which is the
behaviour we want in order to be able to use timers as a means of
synchronization in nf_conntrack.
A later patch will modify __nf_ct_refresh_acct() to use mod_timer_noact()
which will then save one spin_lock_irqsave() / spin_lock_irqrestore() pair per
conntrack timer update. This will also get rid of the race we currently have
without adding more locking in nf_conntrack.
Signed-off-by: Martin Josefsson <gandalf@xxxxxxxxxxxxxx>
---
include/linux/timer.h | 8 ++++++--
kernel/relay.c | 2 +-
kernel/timer.c | 40 +++++++++++++++++++++++++++++++++++-----
3 files changed, 42 insertions(+), 8 deletions(-)
--- a/include/linux/timer.h 2009-02-17 10:55:33.427785986 -0800
+++ b/include/linux/timer.h 2009-02-17 11:04:10.291844534 -0800
@@ -25,6 +25,9 @@ struct timer_list {
extern struct tvec_base boot_tvec_bases;
+#define TIMER_ACT 1
+#define TIMER_NOACT 0
+
#define TIMER_INITIALIZER(_function, _expires, _data) { \
.entry = { .prev = TIMER_ENTRY_STATIC }, \
.function = (_function), \
@@ -86,8 +89,9 @@ static inline int timer_pending(const st
extern void add_timer_on(struct timer_list *timer, int cpu);
extern int del_timer(struct timer_list * timer);
-extern int __mod_timer(struct timer_list *timer, unsigned long expires);
+extern int __mod_timer(struct timer_list *timer, unsigned long expires, int activate);
extern int mod_timer(struct timer_list *timer, unsigned long expires);
+extern int mod_timer_noact(struct timer_list *timer, unsigned long expires);
/*
* The jiffies value which is added to now, when there is no timer
@@ -163,7 +167,7 @@ static inline void timer_stats_timer_cle
static inline void add_timer(struct timer_list *timer)
{
BUG_ON(timer_pending(timer));
- __mod_timer(timer, timer->expires);
+ __mod_timer(timer, timer->expires, TIMER_ACT);
}
#ifdef CONFIG_SMP
--- a/kernel/timer.c 2009-02-17 10:55:33.403580297 -0800
+++ b/kernel/timer.c 2009-02-17 11:04:10.291844534 -0800
@@ -589,7 +589,7 @@ static struct tvec_base *lock_timer_base
}
}
-int __mod_timer(struct timer_list *timer, unsigned long expires)
+int __mod_timer(struct timer_list *timer, unsigned long expires, int activate)
{
struct tvec_base *base, *new_base;
unsigned long flags;
@@ -603,7 +603,8 @@ int __mod_timer(struct timer_list *timer
if (timer_pending(timer)) {
detach_timer(timer, 0);
ret = 1;
- }
+ } else if (activate == TIMER_NOACT)
+ goto out_unlock;
debug_timer_activate(timer);
@@ -629,8 +630,9 @@ int __mod_timer(struct timer_list *timer
timer->expires = expires;
internal_add_timer(base, timer);
- spin_unlock_irqrestore(&base->lock, flags);
+out_unlock:
+ spin_unlock_irqrestore(&base->lock, flags);
return ret;
}
@@ -699,11 +701,39 @@ int mod_timer(struct timer_list *timer,
if (timer->expires == expires && timer_pending(timer))
return 1;
- return __mod_timer(timer, expires);
+ return __mod_timer(timer, expires, TIMER_ACT);
}
EXPORT_SYMBOL(mod_timer);
+/***
+ * mod_timer_noact - modify a timer's timeout
+ * @timer: the timer to be modified
+ *
+ * mod_timer_noact works like mod_timer except that it doesn't activate an
+ * inactive timer, instead it returns without updating timer->expires.
+ *
+ * The function returns whether it has modified a pending timer or not.
+ * (ie. mod_timer_noact() of an inactive timer returns 0, mod_timer_noact() of
+ * an active timer returns 1.)
+ */
+int mod_timer_noact(struct timer_list *timer, unsigned long expires)
+{
+ BUG_ON(!timer->function);
+
+ /*
+ * This is a common optimization triggered by the
+ * networking code - if the timer is re-modified
+ * to be the same thing then just return:
+ */
+ if (timer->expires == expires && timer_pending(timer))
+ return 1;
+
+ return __mod_timer(timer, expires, TIMER_NOACT);
+}
+
+EXPORT_SYMBOL(mod_timer_noact);
+
/**
* del_timer - deactive a timer.
* @timer: the timer to be deactivated
@@ -1268,7 +1298,7 @@ signed long __sched schedule_timeout(sig
expire = timeout + jiffies;
setup_timer_on_stack(&timer, process_timeout, (unsigned long)current);
- __mod_timer(&timer, expire);
+ __mod_timer(&timer, expire, TIMER_ACT);
schedule();
del_singleshot_timer_sync(&timer);
--- a/kernel/relay.c 2009-02-17 10:55:33.416279439 -0800
+++ b/kernel/relay.c 2009-02-17 11:04:10.291844534 -0800
@@ -750,7 +750,7 @@ size_t relay_switch_subbuf(struct rchan_
* from the scheduler (trying to re-grab
* rq->lock), so defer it.
*/
- __mod_timer(&buf->timer, jiffies + 1);
+ __mod_timer(&buf->timer, jiffies + 1, TIMER_NOACT);
}
old = buf->data;
--
--
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