On 02/05/2014 01:41 PM, Thomas Gleixner wrote: > On Wed, 5 Feb 2014, Alexey Perevalov wrote: >> On 02/04/2014 08:10 PM, Thomas Gleixner wrote: >>> On Mon, 27 Jan 2014, Alexey Perevalov wrote: >>>> On 01/21/2014 11:12 PM, John Stultz wrote: >>>>> Thomas: Any thought here? Should we be trying to unify the timerfd flags >>>>> and the posix timer flags (specifically things like TIMER_CANCEL_ON_SET, >>>>> which is currently timerfd-only)? Should a deferrable flag be added to >>>>> the hrtimer core or left to the timer wheel? >>> The timer cancel on set was added only to timerfd because timerfd is a >>> non posix interface and we are halfways free to add stuff to >>> it. Adding extra flags to the real posix timer interfaces is a >>> different story. >> And what about "deferrable" possibility for hrtimers, do you consider it >> reasonable? > In principle, I have no objections, but we need a proper technical > solution. Just adding a flag and keeping the timers in the same rbtree > like we do for the timer wheel timers is not going to happen. > > The only feasible solution is to have separate clock ids, > e.g. CLOCK_*_DEFERRABLE, which would enable the deferrable > functionality for all user space interfaces. No need for magic flags > and complex search for non deferrable timers.
So of course, I was actually arguing against having a new clockid (which was Alexey's first approach). My reasoning was that the deferrablity isn't a clock domain, and is more of a modifier. Thus to keep the interfaces somewhat sane (and avoiding having to add N new clockids for each new modifier), we should utilize the flag arguments to timers. So instead of just having TIMER_ABSTIME, we could add TIMER_DEFER, etc, which we could utilize instead. Internally we can still keep separate bases, much as your patch does, to keep the next-event searching overhead more limited. I mainly wanted to get your thoughts on extending the flags, and doing so in a consistent manner between the timerfd and other timer interfaces. Of course, all this is after I added the _ALARM clockids... so you can decide if its hypocrisy or experience. (The "old wisdom comes from experience and experience comes from bad decisions" bit ;). thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
