2005-04-16 15:20:36 -07:00
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[PATCH] Add debugging feature /proc/timer_stat
Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.
Sample output:
# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
24, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
11, 0 swapper sk_reset_timer (tcp_delack_timer)
6, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
17, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
4, 2050 pcscd do_nanosleep (hrtimer_wakeup)
5, 4179 sshd sk_reset_timer (tcp_write_timer)
4, 2248 yum-updatesd schedule_timeout (process_timeout)
18, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
3, 0 swapper sk_reset_timer (tcp_delack_timer)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
2, 1 swapper e1000_up (e1000_watchdog)
1, 1 init schedule_timeout (process_timeout)
100 total events, 25.24 events/sec
[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-16 01:28:13 -08:00
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2005-04-16 15:20:36 -07:00
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2006-03-31 02:30:30 -08:00
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2005-04-16 15:20:36 -07:00
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2006-03-31 02:30:30 -08:00
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[PATCH] Add debugging feature /proc/timer_stat
Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.
Sample output:
# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
24, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
11, 0 swapper sk_reset_timer (tcp_delack_timer)
6, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
17, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
4, 2050 pcscd do_nanosleep (hrtimer_wakeup)
5, 4179 sshd sk_reset_timer (tcp_write_timer)
4, 2248 yum-updatesd schedule_timeout (process_timeout)
18, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
3, 0 swapper sk_reset_timer (tcp_delack_timer)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
2, 1 swapper e1000_up (e1000_watchdog)
1, 1 init schedule_timeout (process_timeout)
100 total events, 25.24 events/sec
[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-16 01:28:13 -08:00
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2005-04-16 15:20:36 -07:00
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2006-03-31 02:30:30 -08:00
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[PATCH] timers fixes/improvements
This patch tries to solve following problems:
1. del_timer_sync() is racy. The timer can be fired again after
del_timer_sync have checked all cpus and before it will recheck
timer_pending().
2. It has scalability problems. All cpus are scanned to determine
if the timer is running on that cpu.
With this patch del_timer_sync is O(1) and no slower than plain
del_timer(pending_timer), unless it has to actually wait for
completion of the currently running timer.
The only restriction is that the recurring timer should not use
add_timer_on().
3. The timers are not serialized wrt to itself.
If CPU_0 does mod_timer(jiffies+1) while the timer is currently
running on CPU 1, it is quite possible that local interrupt on
CPU_0 will start that timer before it finished on CPU_1.
4. The timers locking is suboptimal. __mod_timer() takes 3 locks
at once and still requires wmb() in del_timer/run_timers.
The new implementation takes 2 locks sequentially and does not
need memory barriers.
Currently ->base != NULL means that the timer is pending. In that case
->base.lock is used to lock the timer. __mod_timer also takes timer->lock
because ->base can be == NULL.
This patch uses timer->entry.next != NULL as indication that the timer is
pending. So it does __list_del(), entry->next = NULL instead of list_del()
when the timer is deleted.
The ->base field is used for hashed locking only, it is initialized
in init_timer() which sets ->base = per_cpu(tvec_bases). When the
tvec_bases.lock is locked, it means that all timers which are tied
to this base via timer->base are locked, and the base itself is locked
too.
So __run_timers/migrate_timers can safely modify all timers which could
be found on ->tvX lists (pending timers).
When the timer's base is locked, and the timer removed from ->entry list
(which means that _run_timers/migrate_timers can't see this timer), it is
possible to set timer->base = NULL and drop the lock: the timer remains
locked.
This patch adds lock_timer_base() helper, which waits for ->base != NULL,
locks the ->base, and checks it is still the same.
__mod_timer() schedules the timer on the local CPU and changes it's base.
However, it does not lock both old and new bases at once. It locks the
timer via lock_timer_base(), deletes the timer, sets ->base = NULL, and
unlocks old base. Then __mod_timer() locks new_base, sets ->base = new_base,
and adds this timer. This simplifies the code, because AB-BA deadlock is not
possible. __mod_timer() also ensures that the timer's base is not changed
while the timer's handler is running on the old base.
__run_timers(), del_timer() do not change ->base anymore, they only clear
pending flag.
So del_timer_sync() can test timer->base->running_timer == timer to detect
whether it is running or not.
We don't need timer_list->lock anymore, this patch kills it.
We also don't need barriers. del_timer() and __run_timers() used smp_wmb()
before clearing timer's pending flag. It was needed because __mod_timer()
did not lock old_base if the timer is not pending, so __mod_timer()->list_add()
could race with del_timer()->list_del(). With this patch these functions are
serialized through base->lock.
One problem. TIMER_INITIALIZER can't use per_cpu(tvec_bases). So this patch
adds global
struct timer_base_s {
spinlock_t lock;
struct timer_list *running_timer;
} __init_timer_base;
which is used by TIMER_INITIALIZER. The corresponding fields in tvec_t_base_s
struct are replaced by struct timer_base_s t_base.
It is indeed ugly. But this can't have scalability problems. The global
__init_timer_base.lock is used only when __mod_timer() is called for the first
time AND the timer was compile time initialized. After that the timer migrates
to the local CPU.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Renaud Lienhart <renaud.lienhart@free.fr>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 00:08:56 -07:00
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2005-04-16 15:20:36 -07:00
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2006-03-31 02:30:30 -08:00
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2005-04-16 15:20:36 -07:00
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2005-09-09 13:10:40 -07:00
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[PATCH] timers fixes/improvements
This patch tries to solve following problems:
1. del_timer_sync() is racy. The timer can be fired again after
del_timer_sync have checked all cpus and before it will recheck
timer_pending().
2. It has scalability problems. All cpus are scanned to determine
if the timer is running on that cpu.
With this patch del_timer_sync is O(1) and no slower than plain
del_timer(pending_timer), unless it has to actually wait for
completion of the currently running timer.
The only restriction is that the recurring timer should not use
add_timer_on().
3. The timers are not serialized wrt to itself.
If CPU_0 does mod_timer(jiffies+1) while the timer is currently
running on CPU 1, it is quite possible that local interrupt on
CPU_0 will start that timer before it finished on CPU_1.
4. The timers locking is suboptimal. __mod_timer() takes 3 locks
at once and still requires wmb() in del_timer/run_timers.
The new implementation takes 2 locks sequentially and does not
need memory barriers.
Currently ->base != NULL means that the timer is pending. In that case
->base.lock is used to lock the timer. __mod_timer also takes timer->lock
because ->base can be == NULL.
This patch uses timer->entry.next != NULL as indication that the timer is
pending. So it does __list_del(), entry->next = NULL instead of list_del()
when the timer is deleted.
The ->base field is used for hashed locking only, it is initialized
in init_timer() which sets ->base = per_cpu(tvec_bases). When the
tvec_bases.lock is locked, it means that all timers which are tied
to this base via timer->base are locked, and the base itself is locked
too.
So __run_timers/migrate_timers can safely modify all timers which could
be found on ->tvX lists (pending timers).
When the timer's base is locked, and the timer removed from ->entry list
(which means that _run_timers/migrate_timers can't see this timer), it is
possible to set timer->base = NULL and drop the lock: the timer remains
locked.
This patch adds lock_timer_base() helper, which waits for ->base != NULL,
locks the ->base, and checks it is still the same.
__mod_timer() schedules the timer on the local CPU and changes it's base.
However, it does not lock both old and new bases at once. It locks the
timer via lock_timer_base(), deletes the timer, sets ->base = NULL, and
unlocks old base. Then __mod_timer() locks new_base, sets ->base = new_base,
and adds this timer. This simplifies the code, because AB-BA deadlock is not
possible. __mod_timer() also ensures that the timer's base is not changed
while the timer's handler is running on the old base.
__run_timers(), del_timer() do not change ->base anymore, they only clear
pending flag.
So del_timer_sync() can test timer->base->running_timer == timer to detect
whether it is running or not.
We don't need timer_list->lock anymore, this patch kills it.
We also don't need barriers. del_timer() and __run_timers() used smp_wmb()
before clearing timer's pending flag. It was needed because __mod_timer()
did not lock old_base if the timer is not pending, so __mod_timer()->list_add()
could race with del_timer()->list_del(). With this patch these functions are
serialized through base->lock.
One problem. TIMER_INITIALIZER can't use per_cpu(tvec_bases). So this patch
adds global
struct timer_base_s {
spinlock_t lock;
struct timer_list *running_timer;
} __init_timer_base;
which is used by TIMER_INITIALIZER. The corresponding fields in tvec_t_base_s
struct are replaced by struct timer_base_s t_base.
It is indeed ugly. But this can't have scalability problems. The global
__init_timer_base.lock is used only when __mod_timer() is called for the first
time AND the timer was compile time initialized. After that the timer migrates
to the local CPU.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Renaud Lienhart <renaud.lienhart@free.fr>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 00:08:56 -07:00
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2007-05-08 00:27:44 -07:00
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2005-04-16 15:20:36 -07:00
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2005-10-30 15:01:38 -08:00
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2007-01-26 00:57:09 -08:00
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2005-04-16 15:20:36 -07:00
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[PATCH] timers fixes/improvements
This patch tries to solve following problems:
1. del_timer_sync() is racy. The timer can be fired again after
del_timer_sync have checked all cpus and before it will recheck
timer_pending().
2. It has scalability problems. All cpus are scanned to determine
if the timer is running on that cpu.
With this patch del_timer_sync is O(1) and no slower than plain
del_timer(pending_timer), unless it has to actually wait for
completion of the currently running timer.
The only restriction is that the recurring timer should not use
add_timer_on().
3. The timers are not serialized wrt to itself.
If CPU_0 does mod_timer(jiffies+1) while the timer is currently
running on CPU 1, it is quite possible that local interrupt on
CPU_0 will start that timer before it finished on CPU_1.
4. The timers locking is suboptimal. __mod_timer() takes 3 locks
at once and still requires wmb() in del_timer/run_timers.
The new implementation takes 2 locks sequentially and does not
need memory barriers.
Currently ->base != NULL means that the timer is pending. In that case
->base.lock is used to lock the timer. __mod_timer also takes timer->lock
because ->base can be == NULL.
This patch uses timer->entry.next != NULL as indication that the timer is
pending. So it does __list_del(), entry->next = NULL instead of list_del()
when the timer is deleted.
The ->base field is used for hashed locking only, it is initialized
in init_timer() which sets ->base = per_cpu(tvec_bases). When the
tvec_bases.lock is locked, it means that all timers which are tied
to this base via timer->base are locked, and the base itself is locked
too.
So __run_timers/migrate_timers can safely modify all timers which could
be found on ->tvX lists (pending timers).
When the timer's base is locked, and the timer removed from ->entry list
(which means that _run_timers/migrate_timers can't see this timer), it is
possible to set timer->base = NULL and drop the lock: the timer remains
locked.
This patch adds lock_timer_base() helper, which waits for ->base != NULL,
locks the ->base, and checks it is still the same.
__mod_timer() schedules the timer on the local CPU and changes it's base.
However, it does not lock both old and new bases at once. It locks the
timer via lock_timer_base(), deletes the timer, sets ->base = NULL, and
unlocks old base. Then __mod_timer() locks new_base, sets ->base = new_base,
and adds this timer. This simplifies the code, because AB-BA deadlock is not
possible. __mod_timer() also ensures that the timer's base is not changed
while the timer's handler is running on the old base.
__run_timers(), del_timer() do not change ->base anymore, they only clear
pending flag.
So del_timer_sync() can test timer->base->running_timer == timer to detect
whether it is running or not.
We don't need timer_list->lock anymore, this patch kills it.
We also don't need barriers. del_timer() and __run_timers() used smp_wmb()
before clearing timer's pending flag. It was needed because __mod_timer()
did not lock old_base if the timer is not pending, so __mod_timer()->list_add()
could race with del_timer()->list_del(). With this patch these functions are
serialized through base->lock.
One problem. TIMER_INITIALIZER can't use per_cpu(tvec_bases). So this patch
adds global
struct timer_base_s {
spinlock_t lock;
struct timer_list *running_timer;
} __init_timer_base;
which is used by TIMER_INITIALIZER. The corresponding fields in tvec_t_base_s
struct are replaced by struct timer_base_s t_base.
It is indeed ugly. But this can't have scalability problems. The global
__init_timer_base.lock is used only when __mod_timer() is called for the first
time AND the timer was compile time initialized. After that the timer migrates
to the local CPU.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Renaud Lienhart <renaud.lienhart@free.fr>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 00:08:56 -07:00
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2005-04-16 15:20:36 -07:00
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2007-05-29 23:47:39 +02:00
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2007-02-16 01:27:47 -08:00
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2005-04-16 15:20:36 -07:00
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2007-02-16 01:27:47 -08:00
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2005-04-16 15:20:36 -07:00
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[PATCH] Add debugging feature /proc/timer_stat
Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.
Sample output:
# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
24, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
11, 0 swapper sk_reset_timer (tcp_delack_timer)
6, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
17, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
4, 2050 pcscd do_nanosleep (hrtimer_wakeup)
5, 4179 sshd sk_reset_timer (tcp_write_timer)
4, 2248 yum-updatesd schedule_timeout (process_timeout)
18, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
3, 0 swapper sk_reset_timer (tcp_delack_timer)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
2, 1 swapper e1000_up (e1000_watchdog)
1, 1 init schedule_timeout (process_timeout)
100 total events, 25.24 events/sec
[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-16 01:28:13 -08:00
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2007-07-15 23:40:30 -07:00
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[PATCH] Add debugging feature /proc/timer_stat
Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.
Sample output:
# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
24, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
11, 0 swapper sk_reset_timer (tcp_delack_timer)
6, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
17, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
4, 2050 pcscd do_nanosleep (hrtimer_wakeup)
5, 4179 sshd sk_reset_timer (tcp_write_timer)
4, 2248 yum-updatesd schedule_timeout (process_timeout)
18, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
3, 0 swapper sk_reset_timer (tcp_delack_timer)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
2, 1 swapper e1000_up (e1000_watchdog)
1, 1 init schedule_timeout (process_timeout)
100 total events, 25.24 events/sec
[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-16 01:28:13 -08:00
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2007-07-15 23:40:30 -07:00
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[PATCH] Add debugging feature /proc/timer_stat
Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.
Sample output:
# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
24, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
11, 0 swapper sk_reset_timer (tcp_delack_timer)
6, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
17, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
4, 2050 pcscd do_nanosleep (hrtimer_wakeup)
5, 4179 sshd sk_reset_timer (tcp_write_timer)
4, 2248 yum-updatesd schedule_timeout (process_timeout)
18, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
3, 0 swapper sk_reset_timer (tcp_delack_timer)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
2, 1 swapper e1000_up (e1000_watchdog)
1, 1 init schedule_timeout (process_timeout)
100 total events, 25.24 events/sec
[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-16 01:28:13 -08:00
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2007-01-26 00:57:09 -08:00
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2005-04-16 15:20:36 -07:00
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2006-03-24 18:13:37 +01:00
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2005-04-16 15:20:36 -07:00
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2006-03-24 18:13:37 +01:00
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2005-04-16 15:20:36 -07:00
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2006-03-24 18:13:37 +01:00
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2005-04-16 15:20:36 -07:00
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2005-10-30 15:02:24 -08:00
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2005-04-16 15:20:36 -07:00
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2005-10-30 15:02:24 -08:00
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2005-04-16 15:20:36 -07:00
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2005-06-23 00:08:59 -07:00
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2005-04-16 15:20:36 -07:00
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2005-06-23 00:08:59 -07:00
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2005-04-16 15:20:36 -07:00
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[PATCH] timers fixes/improvements
This patch tries to solve following problems:
1. del_timer_sync() is racy. The timer can be fired again after
del_timer_sync have checked all cpus and before it will recheck
timer_pending().
2. It has scalability problems. All cpus are scanned to determine
if the timer is running on that cpu.
With this patch del_timer_sync is O(1) and no slower than plain
del_timer(pending_timer), unless it has to actually wait for
completion of the currently running timer.
The only restriction is that the recurring timer should not use
add_timer_on().
3. The timers are not serialized wrt to itself.
If CPU_0 does mod_timer(jiffies+1) while the timer is currently
running on CPU 1, it is quite possible that local interrupt on
CPU_0 will start that timer before it finished on CPU_1.
4. The timers locking is suboptimal. __mod_timer() takes 3 locks
at once and still requires wmb() in del_timer/run_timers.
The new implementation takes 2 locks sequentially and does not
need memory barriers.
Currently ->base != NULL means that the timer is pending. In that case
->base.lock is used to lock the timer. __mod_timer also takes timer->lock
because ->base can be == NULL.
This patch uses timer->entry.next != NULL as indication that the timer is
pending. So it does __list_del(), entry->next = NULL instead of list_del()
when the timer is deleted.
The ->base field is used for hashed locking only, it is initialized
in init_timer() which sets ->base = per_cpu(tvec_bases). When the
tvec_bases.lock is locked, it means that all timers which are tied
to this base via timer->base are locked, and the base itself is locked
too.
So __run_timers/migrate_timers can safely modify all timers which could
be found on ->tvX lists (pending timers).
When the timer's base is locked, and the timer removed from ->entry list
(which means that _run_timers/migrate_timers can't see this timer), it is
possible to set timer->base = NULL and drop the lock: the timer remains
locked.
This patch adds lock_timer_base() helper, which waits for ->base != NULL,
locks the ->base, and checks it is still the same.
__mod_timer() schedules the timer on the local CPU and changes it's base.
However, it does not lock both old and new bases at once. It locks the
timer via lock_timer_base(), deletes the timer, sets ->base = NULL, and
unlocks old base. Then __mod_timer() locks new_base, sets ->base = new_base,
and adds this timer. This simplifies the code, because AB-BA deadlock is not
possible. __mod_timer() also ensures that the timer's base is not changed
while the timer's handler is running on the old base.
__run_timers(), del_timer() do not change ->base anymore, they only clear
pending flag.
So del_timer_sync() can test timer->base->running_timer == timer to detect
whether it is running or not.
We don't need timer_list->lock anymore, this patch kills it.
We also don't need barriers. del_timer() and __run_timers() used smp_wmb()
before clearing timer's pending flag. It was needed because __mod_timer()
did not lock old_base if the timer is not pending, so __mod_timer()->list_add()
could race with del_timer()->list_del(). With this patch these functions are
serialized through base->lock.
One problem. TIMER_INITIALIZER can't use per_cpu(tvec_bases). So this patch
adds global
struct timer_base_s {
spinlock_t lock;
struct timer_list *running_timer;
} __init_timer_base;
which is used by TIMER_INITIALIZER. The corresponding fields in tvec_t_base_s
struct are replaced by struct timer_base_s t_base.
It is indeed ugly. But this can't have scalability problems. The global
__init_timer_base.lock is used only when __mod_timer() is called for the first
time AND the timer was compile time initialized. After that the timer migrates
to the local CPU.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Renaud Lienhart <renaud.lienhart@free.fr>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 00:08:56 -07:00
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2005-04-16 15:20:36 -07:00
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2006-03-26 01:38:12 -08:00
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2007-02-16 01:27:49 -08:00
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2005-04-16 15:20:36 -07:00
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2006-12-10 02:21:24 -08:00
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2005-04-16 15:20:36 -07:00
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