Messages in this thread | | | Date | Fri, 23 Sep 2005 08:21:41 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [ANNOUNCE] ktimers subsystem |
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On Fri, Sep 23, 2005 at 01:09:46AM +0200, Roman Zippel wrote: > On Thu, 22 Sep 2005, Thomas Gleixner wrote:
[ . . . ]
> > > The main difference between them is that the latter is user > > > programmable. > > > > wallclock is reprogrammable too and it introduces a bunch of horrible > > functions in posix-timers.c. grep for abs_list. I explained why its > > horrible already. > > I said _user_ programmable, wallclock time is usually NTP controlled.
I believe Thomas is concerned about workloads that need a short-term stable timebase. For example, a process-control application might need to accurately measure a (say) 1500-millisecond time interval. Both user-programmability and NTP adjustments to a given timebase could destroy the needed measurement accuracy.
Such a workload does not need the long-term tie to wallclock time that NTP provides, but it does need the accurate short-term timekeeping that NTP cannot provide -- NTP sacrifices short-term accuracy in order to adjust the clock as needed to gain long-term stability.
Thomas, John, please jump in if I am missing the point here.
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