Re: [PATCH 0/3] Deferrable timers support for timerfd API

[Alexey Perevalov]

On 01/04/2014 04:18 AM, John Stultz wrote:
> On 01/03/2014 09:45 AM, Alexey Perevalov wrote:
> > On 01/03/2014 03:17 AM, John Stultz wrote:
> > > On 01/02/2014 10:30 AM, Alexey Perevalov wrote:
> > > > This version introduces new clockid (CLOCK_DEFERRABLE) , for
> > > > timerfd_create, instead of
> > > > new flag (TFD_TIMER_DEFERRABLE) for timerfd_settime introduced in
> > > > previous version.
> > > So why did you make this change?
> > >
> > > thanks
> > > -john
> > I looked at alarm timers and found approach of making timer behavior
> > persistent per file descriptor is better than
> > changeable by timerfd_settime. I think "end user wake up from suspend"
> > and "don't wake up in idle" is the same thing on the same abstraction
> > level.
> >
> > Yes Anton's previous  patches worked with CLOCK_MONOTONIC only and I
> > didn't intend to use it with CLOCK_REALTIME, cause it's hard to me to
> > find such use case.
> > Another way - it's stay as was Anton's patch, I mean as flag for the
> > timerfd_settime, but in original patch set both hrtimer and deferrable
> > timers initialized in timerfd_create, I think it's not needed. Also
> > ability to change timer behavior looks not good if you couldn't change
> > alarm timer behavior, not unified API.
> So while the alarm timers are a reasonable precedent, I think they were
> introduced prior to the timerfd interface, so it seemed at the time
> having new clockids for the functionality was required to work with the
> existing syscalls that use the clockid (Though in retrospect, I question
> if it would have been better to use timer flags to introduce the alarm
> functionality rather then introducing it via a clockid, as it would
> simplify the clockid definitions).
As I understood alarm and deferrability it's type of repetition (timer 
trigger condition),
but REALTIME, BOOTTIME, MONOTONIC it's a type of time representation.
Mixed it in one clockid, maybe it's a controversially. Which flags do 
you want to use, flags of timerfd_settime?

> Now that we have the timerfd interface, and if this functionality is
> really limited to the timerfds, then we may want to consider what might
> be, at least to me, the cleaner approach of using the flag.
>
> Either way, I'd like to make sure we have a sound rational. My worry is
> that deferrable timers would be desired on more then just
> CLOCK_MONOTONIC, so we could quite likely end up with quite a few new
> clockids (ie: CLOCK_BOOTTIME_DEFERRED, CLOCK_TAI_DEFERRED,
> CLOCK_REALTIME_DEFERRED).
Here I'm totally agree CLOCK_DEFERRABLE is not maintainable named constant.


> > If I'm right, only high resolution timer could be REALTIME, and there
> > is no deferrable behavior for hrtimer only for timer_list.
> I'm not sure I understood this part. Could you explain further?
I meant, we couldn't use hrtimer for deferrability, right now.

> thanks
> -john


--
Best regards,
Alexey Perevalov
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