linux-kernel - Re: RFC: better timer interface

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Message-ID: <CAK8P3a1FoR_usw7du3ZRMF+PPhJ712EpArL_e1bLVNs7BYBu-w@mail.gmail.com>
Date:   Tue, 16 May 2017 17:45:07 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@....de>
Cc:     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 1:48 PM, Christoph Hellwig <hch@....de> wrote:
> Hi all,
>
> this series attempts to provide a "modern" timer interface where the
> callback gets the timer_list structure as an argument so that it
> can use container_of instead of having to cast to/from unsigned long
> all the time (or even worse use function pointer casts, we have quite
> a few of those as well).

This looks really nice, but what is the long-term plan for the interface?
Do you expect that we will eventually change all 700+ users of timer_list
to the new type, or do we keep both variants around indefinitely to avoid
having to do mass-conversions?

If we are going to touch them all in the end, we might want to think
about other changes that could be useful here. The main one I have
in mind would be moving away from 'jiffies + timeout' as the interface,
and instead passing a relative number of milliseconds (or seconds)
into a mod_timer() variant. This is what most drivers want anyway,
and if we have both changes (callback argument and expiration
time) in place, we modernize the API one driver at a time with both
changes at once.

      Arnd