Date: Thu, 10 Sep 1998 11:45:15 +1200
From: Chris Wedgwood <chris@cybernet.co.nz>
To: Colin Plumb <colin@nyx.net>, tytso@MIT.EDU
Cc: andrejp@luz.fe.uni-lj.si, linux-kernel@vger.rutgers.edu
Subject: Re: GPS Leap Second Scheduled!
Message-ID: <19980910114515.A20254@caffeine.ix.net.nz>
References: <199809092013.OAA10252@nyx10.nyx.net>
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In-Reply-To: <199809092013.OAA10252@nyx10.nyx.net>; from Colin Plumb on Wed, Sep 09, 1998 at 02:13:42PM -0600
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On Wed, Sep 09, 1998 at 02:13:42PM -0600, Colin Plumb wrote:

> - gettimeofday() never returns the same value twice (documented BSD
>   behaviour)

Ouch... gettimeofday(2) only presently has usec resolution. I suspect
we can make this report the same value twice on really high end boxes
(667MHz Alpha maybe, 400Mhz Sparcs?), if not now, in a year or so.
Even a P.ii 600 or so can probably manage it.

Sure... this is fixable and not hard to fix, but it requires breaking
binary compatibility.

The attached code on a PPro 200 gives me results of 2 usecs, using a
P.II 300 and SYSENTER semantics, you can probably get this to less
that 1usec.

> I don't know of a pretty way.  What I'd like, as I said, is a
> defined kludge, so that there is a defined mapping between struct
> timeval and struct timespec and UTC in the vicinity of a leap
> second.

I'm not sure about a sane kludge for mapping to/from the semantics we
already have, but how about we just declare the existing API buggy
under some (rare circumstances) and create a new one with flags to
show whether or not a leap second is currently under way, much the
same as is done for daylight savings time with time zones. (You can
have two 2:30ams, only one of which tough is DST, the other is
non-DST).


-Chris

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