linux-kernel - Re: RFC: better timer interface

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Message-ID: <20170518082703.GD3812@lst.de>
Date:   Thu, 18 May 2017 10:27:03 +0200
From:   Christoph Hellwig <hch@....de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Mark Gross <mark.gross@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>
Subject: Re: RFC: better timer interface

On Tue, May 16, 2017 at 10:26:39PM +0200, Arnd Bergmann wrote:
> If we keep the unusual *_timer() naming (rather than timer_*() as hrtimer
> has), we could use one of
> 
> a) start_timer(struct timer_list *timer, unsigned long ms);
> b) restart_timer(struct timer_list *timer, unsigned long ms);
> c) mod_timer_ms(struct timer_list *timer, unsigned long ms);
>     mod_timer_sec(struct timer_list *timer, unsigned long sec);
> 
> The first is slightly shorter but conflicts with three files that use
> the same name for a local function name. The third one fits
> well with the existing interfaces and provides both millisecond
> and second versions, I'd probably go with that.

Yeah, I'd take c) as well.  I'll give it a spin.

> We could consider even passing a default interval as another
> argument to prepare_timer(), and using that in add_timer(),
> but that would in those cases that have a constant interval
> (maybe about half of the users from) and would be a bit surprising
> to readers that are only familiar with the existing interfaces.

That seems rather ugly to me.

> One final option would be a larger-scale replacement of
> the API by mirroring the hrtimer style where possible while
> staying compatible with the existing calls, e.g. timer_prepare(),
> timer_add_expires(), timer_start(), ...

I'd chose timer_* for an entirely new API, but at this point this
seems a bit too much churn to me.