Message-ID: <424D5207.3E57CBCA@tv-sign.ru>
Date: Fri, 01 Apr 2005 17:52:07 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
MIME-Version: 1.0
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
       Christoph Lameter <christoph@lameter.com>,
       "Chen, Kenneth W" <kenneth.w.chen@intel.com>,
       Andrew Morton <akpm@osdl.org>
Subject: Re: [RFC][PATCH] timers fixes/improvements
References: <424D373F.1BCBF2AC@tv-sign.ru> <424D37B2.2CE24C67@tv-sign.ru> <20050401130713.GA3802@elte.hu>
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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.
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