From: Szabolcs Nagy <nsz@port70.net>
To: musl@lists.openwall.com
Subject: Re: [PATCHv2] Add support for leap seconds in zoneinfo files
Date: Sat, 7 Dec 2013 05:02:06 +0100 [thread overview]
Message-ID: <20131207040205.GE1685@port70.net> (raw)
In-Reply-To: <20131207023114.GK24286@brightrain.aerifal.cx>
* Rich Felker <dalias@aerifal.cx> [2013-12-06 21:31:14 -0500]:
> On Fri, Dec 06, 2013 at 11:29:33PM +0000, Laurent Bercot wrote:
> > On 06/12/2013 11:38, Raphael Cohn wrote:
> > >Date and time match has been got wrong in every system
> > >(...)
> > >Personally, I think apps should just use a monotonic source of seconds
> > > from an epoch, and use a well-developed third party lib dedicated to
> > > the problem if they need date math (eg Joda time in Java).
> >
> > I absolutely agree with you on the first part. I disagree on the second
> > part. Dealing with time shouldn't be a burden on the application - devs
> > have other things to think about, and experience shows that most of them
> > won't care, they'll just use the primitives provided by the system. So,
> > the system should do the right thing, i.e. provide something that works
> > no matter how applications are using it. Here, it means providing a
> > linear CLOCK_REALTIME, because people use it as if it were CLOCK_MONOTONIC.
>
> If that's your only goal, it's easily achieved without storing TAI-10
> in the CLOCK_REALTIME clock, assuming by "linear" you just mean
> "monotonic, continuous, and accurate within the margin of measurement
> error". Discontinuous jumps and non-monotonicity in CLOCK_REALTIME
> were a monstrosity invented by the NTPD folks in their implementation
> for mapping TAI onto POSIX time, not any fundamental requirement.
it's worse than that, the proposed solution does put a burden on userspace
(unix time can no longer be used to calculate or represent dates)
while with the standard 1 day == 86400 s apps and admins do not even need
to know about leapseconds (only the time daemon and kernel)
about linearity:
if you only smooth out a leapsecond in the month it was inserted, then a
unix second would be about 30*86400/(30*86400+1)-1 = -0.386 ppm (= 386ns)
shorter than a SI second in that month, by comparision (according to the
ntp clock quality faq) the oscillator used by most hw usually have more
than 1 ppm frequency error and it can change 1 ppm/C when heated up if no
temperature correction is done, so apps already have to deal with larger
errors and the smoothing logic is in the kernel/ntpd they just don't apply
it to leapseconds
this will work for more than 1000 years (earth rotation drift is <12s/year)
and somewhere during that time leapseconds will be abolished and it stops
being a problem..
next prev parent reply other threads:[~2013-12-07 4:02 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-26 18:53 [PATCH] " Laurent Bercot
2013-11-26 18:59 ` Laurent Bercot
2013-11-26 23:32 ` Rich Felker
2013-11-27 1:06 ` Rich Felker
2013-11-27 4:10 ` Laurent Bercot
2013-11-27 4:25 ` Rich Felker
2013-11-27 5:53 ` Laurent Bercot
2013-11-27 18:43 ` Szabolcs Nagy
2013-11-27 20:33 ` Laurent Bercot
2013-12-05 1:13 ` [PATCHv2] " Laurent Bercot
2013-12-05 5:18 ` Szabolcs Nagy
2013-12-05 8:58 ` Laurent Bercot
2013-12-05 14:21 ` Szabolcs Nagy
2013-12-05 14:43 ` Rich Felker
2013-12-05 16:31 ` Laurent Bercot
2013-12-05 16:40 ` Rich Felker
2013-12-06 0:36 ` Laurent Bercot
2013-12-06 0:45 ` Rich Felker
2013-12-06 1:15 ` Laurent Bercot
2013-12-06 5:31 ` Szabolcs Nagy
2013-12-06 10:48 ` Laurent Bercot
2013-12-06 11:38 ` Raphael Cohn
2013-12-06 23:29 ` Laurent Bercot
2013-12-07 2:31 ` Rich Felker
2013-12-07 4:02 ` Szabolcs Nagy [this message]
2013-12-07 8:52 ` Laurent Bercot
2013-12-06 6:29 ` Rich Felker
2013-12-06 10:37 ` Laurent Bercot
2013-12-06 12:50 ` Rich Felker
2013-12-06 13:27 ` Szabolcs Nagy
2013-12-06 15:48 ` Rich Felker
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