Messages in this thread | | | Date | Wed, 14 Dec 2011 19:21:21 +0100 | From | Richard Cochran <> | Subject | Re: [RFC 0/2] ABI for clock_gettime_ns |
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On Wed, Dec 14, 2011 at 08:23:52AM -0800, john stultz wrote: > On Wed, 2011-12-14 at 08:20 +0100, Richard Cochran wrote: > > Michel Hack wrote an article last year detailing how Linux botches the > > leap second and suggested a more robust way to handle it. > > Hmm. Do you have a link to the article?
I don't think it is online. Do you have the magic IEEE access?
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5609776
> I like the idea of having TAI as a kernel clockid. The hard part is > getting systems to initialize it properly at boot. > > Also part of the issue with leapseconds is that time functions are such > a hot path, we can't really add extra conditionals checking for leap > seconds. Instead the leapsecond occurs on the first tick of the > leapsecond.
The idea would only involve one conditional and one addition:
- System clock represents TAI - Table of {threshold; offset} values, read mostly, rarely updated - Table has index pointing to next event
Get time becomes:
1. read system time 2. test threshold 3. apply correction
> More interestingly to me is Google's recent use of slewed leapseconds. > However, how that would work on a public network is a bit more fuzzy. > And being able to support both TAI and slewed leapseconds would require > quite a bit more logic.
Do you mean smoothing the jump over the entire day (or other interval)? This is also discussed in Hack's paper.
Thanks, Richard
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