Messages in this thread Patch in this message | | | Date | Wed, 30 Nov 2005 03:32:45 +0100 (CET) | From | Roman Zippel <> | Subject | Re: [PATCH 1/9] timer locking optimization |
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Hi,
On Tue, 29 Nov 2005, Oleg Nesterov wrote:
> Also, you have wrong value of 'base' after 'goto restart'.
Here is the updated patch, which fixes this.
bye, Roman
Index: linux-2.6/kernel/timer.c =================================================================== --- linux-2.6.orig/kernel/timer.c 2005-11-29 13:29:35.000000000 +0100 +++ linux-2.6/kernel/timer.c 2005-11-29 14:01:42.000000000 +0100 @@ -178,27 +178,20 @@ static inline void detach_timer(struct t * * So __run_timers/migrate_timers can safely modify all timers which could * be found on ->tvX lists. - * - * When the timer's base is locked, and the timer removed from list, it is - * possible to set timer->base = NULL and drop the lock: the timer remains - * locked. */ static timer_base_t *lock_timer_base(struct timer_list *timer, unsigned long *flags) { timer_base_t *base; - for (;;) { - base = timer->base; - if (likely(base != NULL)) { - spin_lock_irqsave(&base->lock, *flags); - if (likely(base == timer->base)) - return base; - /* The timer has migrated to another CPU */ - spin_unlock_irqrestore(&base->lock, *flags); - } - cpu_relax(); - } +again: + base = timer->base; + spin_lock_irqsave(&base->lock, *flags); + if (likely(base == timer->base)) + return base; + /* The timer has migrated to another CPU */ + spin_unlock_irqrestore(&base->lock, *flags); + goto again; } int __mod_timer(struct timer_list *timer, unsigned long expires) @@ -210,6 +203,7 @@ int __mod_timer(struct timer_list *timer BUG_ON(!timer->function); +restart: base = lock_timer_base(timer, &flags); if (timer_pending(timer)) { @@ -231,11 +225,18 @@ int __mod_timer(struct timer_list *timer /* The timer remains on a former base */ new_base = container_of(base, tvec_base_t, t_base); } else { - /* See the comment in lock_timer_base() */ - timer->base = NULL; + /* + * We shortly release the timer and the timer can + * migrate to another cpu, so recheck the base after + * getting the lock. + */ + timer->base = &new_base->t_base; spin_unlock(&base->lock); spin_lock(&new_base->t_base.lock); - timer->base = &new_base->t_base; + if (unlikely(timer->base != &new_base->t_base)) { + spin_unlock_irqrestore(&new_base->t_base.lock, flags); + goto restart; + } } } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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