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timers: Cache __next_timer_interrupt result

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Each time a cpu goes to sleep on a NOHZ=y system the timer
wheel is searched for the next timer interrupt. It can take
quite a few cycles to find the next pending timer.

This patch adds a field to tvec_base that caches the result of
__next_timer_interrupt.

The hit ratio is around 80% on my thinkpad under normal use, on
a server I've seen hit ratios from 5% to 95% dependent on the
workload.

-v2: jiffies wrap fixes

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com>
LKML-Reference: <20090721202505.7d56a079@skybase>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Martin Schwidefsky 2009-07-21 20:25:05 +02:00 committed by Ingo Molnar
parent fbd90375d7
commit 97fd9ed48c
1 changed files with 23 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
kernel/timer.c
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@ -72,6 +72,7 @@ struct tvec_base {
spinlock_t lock;
struct timer_list *running_timer;
unsigned long timer_jiffies;
unsigned long next_timer;
struct tvec_root tv1;
struct tvec tv2;
struct tvec tv3;
@ -622,6 +623,9 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
if (timer_pending(timer)) {
detach_timer(timer, 0);
if (timer->expires == base->next_timer &&
!tbase_get_deferrable(timer->base))
base->next_timer = base->timer_jiffies;
ret = 1;
} else {
if (pending_only)
@ -663,6 +667,9 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
}
timer->expires = expires;
if (time_before(timer->expires, base->next_timer) &&
!tbase_get_deferrable(timer->base))
base->next_timer = timer->expires;
internal_add_timer(base, timer);
out_unlock:
@ -781,6 +788,9 @@ void add_timer_on(struct timer_list *timer, int cpu)
spin_lock_irqsave(&base->lock, flags);
timer_set_base(timer, base);
debug_timer_activate(timer);
if (time_before(timer->expires, base->next_timer) &&
!tbase_get_deferrable(timer->base))
base->next_timer = timer->expires;
internal_add_timer(base, timer);
/*
* Check whether the other CPU is idle and needs to be
@ -817,6 +827,9 @@ int del_timer(struct timer_list *timer)
base = lock_timer_base(timer, &flags);
if (timer_pending(timer)) {
detach_timer(timer, 1);
if (timer->expires == base->next_timer &&
!tbase_get_deferrable(timer->base))
base->next_timer = base->timer_jiffies;
ret = 1;
}
spin_unlock_irqrestore(&base->lock, flags);
@ -850,6 +863,9 @@ int try_to_del_timer_sync(struct timer_list *timer)
ret = 0;
if (timer_pending(timer)) {
detach_timer(timer, 1);
if (timer->expires == base->next_timer &&
!tbase_get_deferrable(timer->base))
base->next_timer = base->timer_jiffies;
ret = 1;
}
out:
@ -1134,7 +1150,9 @@ unsigned long get_next_timer_interrupt(unsigned long now)
unsigned long expires;
spin_lock(&base->lock);
expires = __next_timer_interrupt(base);
if (time_before_eq(base->next_timer, base->timer_jiffies))
base->next_timer = __next_timer_interrupt(base);
expires = base->next_timer;
spin_unlock(&base->lock);
if (time_before_eq(expires, now))
@ -1523,6 +1541,7 @@ static int __cpuinit init_timers_cpu(int cpu)
INIT_LIST_HEAD(base->tv1.vec + j);
base->timer_jiffies = jiffies;
base->next_timer = base->timer_jiffies;
return 0;
}
@ -1535,6 +1554,9 @@ static void migrate_timer_list(struct tvec_base *new_base, struct list_head *hea
timer = list_first_entry(head, struct timer_list, entry);
detach_timer(timer, 0);
timer_set_base(timer, new_base);
if (time_before(timer->expires, new_base->next_timer) &&
!tbase_get_deferrable(timer->base))
new_base->next_timer = timer->expires;
internal_add_timer(new_base, timer);
}
}