Re: [RFC][PATCH] timers fixes/improvements

[Oleg Nesterov <oleg@tv-sign.ru>]

Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@tv-sign.ru> wrote:
>
> > struct timer_list {
> > 	...
> > 	timer_base_t *_base;
> > };
>
> namespace cleanliness: i'd suggest s/_base/base.

I deliberately renamed it to '_base' because then it is much more grepable.
But I don't mind doing s/_base/base/ if you prefer.

> > int __mod_timer(struct timer_list *timer, unsigned long expires)
> [...]
> > 		/* Ensure the timer is serialized. */
> > 		if (base != &new_base->t_base
> > 			&& base->running_timer == timer)
> > 			goto unlock;
>
> > unlock:
> > 		spin_unlock_irqrestore(&base->lock, flags);
> > 	} while (ret < 0);
>
> so we keep looping in __mod_timer() when the timer is running? Couldnt
> this be a performance hit?

I hope it is unlikely that __mod_timer() would hit the already running timer,
so hopefully this will not degrade the performance. And I don't see a simple
alternative to ensure the timer's serialization. At least it spins without
interrupts disabling.

Oleg.