linux-kernel - Re: [RFC] mod_timer() helper functions?

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Date:	Sat, 16 May 2009 23:03:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Chris Peterson <cpeterso@...terso.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [RFC] mod_timer() helper functions?

On Sat, 16 May 2009 00:36:15 -0700 Chris Peterson <cpeterso@...terso.com> wrote:

> Reviewing the kernel's nearly one-thousand calls to mod_timer(), there
> are three basic patterns:
> 
>  * multi-second timeouts
>  * millisecond timeouts
>  * +1 jiffie ASAP events
> 
> Few mod_timer() calls actually use the function's 'expires' deadline
> time without manually calculating 'jiffies + delay'. The following
> helper functions could provide a simpler, more descriptive interface
> than the low-level mod_timer() function. Also, when scheduling longer
> timers, these helper functions could use round_jiffies() to (secretly)
> batch timers on whole seconds to reduce power usage.
> 
> Any suggestions? Is there enough value to warrant adding helper
> function like these as an alternative to mod_timer()?
> 
> 
> chris
> 
> ---
> static inline int mod_timer_seconds(struct timer_list *timer, time_t seconds)
> {
> 	return mod_timer(timer, round_jiffies(jiffies + seconds * HZ));
> }
> 
> static inline int mod_timer_msecs(struct timer_list *timer, unsigned int msecs)
> {
> 	/* TODO? Round jiffies if within some epsilon of a whole second? */
> 	return mod_timer(timer, jiffies + msecs_to_jiffies(msecs));
> }
> 
> static inline int mod_timer_yield(struct timer_list *timer)
> {
> 	/* After these messages, we'll be right back. */
> 	return mod_timer(timer, jiffies + 1);
> }

I think it makes sense, yes.

I do think that the name should be changed to communicate the fact that
the change is relative.  advance_timer_foo(), perhaps.

Or, if you want to put lipstick on our pig, timer_advance_foo().  All
these API functions should have started with "timer_" but we screwed
that up ages ago.

I expect that most/all of these functions will be too large to inline,
btw.  Check the generated code and I expect you'll be surprised how
porky they are.
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