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    SubjectRe: [RFC 0/2] ABI for clock_gettime_ns
    On Mon, Dec 12, 2011 at 7:43 PM, john stultz <johnstul@us.ibm.com> wrote:
    > On Tue, 2011-12-13 at 04:24 +0100, Richard Cochran wrote:
    >> On Mon, Dec 12, 2011 at 05:26:36PM -0800, Andy Lutomirski wrote:
    >> > On x86-64, clock_gettime is so fast that the overhead converting to and
    >> > from nanoseconds is non-negligible.  clock_gettime_ns is a different
    >> > interface that is potentially faster.  If people like the ABI, I'll
    >> > implement an optimized version.
    >>
    >> I am not so interested in performance optimizations, but do I think
    >> offering time in nanoseconds is attractive from an application point
    >> of view. The timespec is impractical for everyone.
    >>
    >> While you are at it with new syscalls, why not make a clean break from
    >> POSIX and fix the uglies?
    >>
    >> - New name, to distance ourselves from POSIX (clock_ns_get?)

    I will defer to the bikeshedding consensus :)

    >> - Family of calls, with set/get

    Setting the time is a big can of worms. adjtimex is rather
    incomprehensible (without reading lots of source and/or the rfc) and
    IMO puts a lot of NTP magic into the kernel, where it doesn't belong.
    But I don't really want to design, let alone implement, something
    better, especially right now. Maybe a better design would let you
    open a file descriptor to control the time and apply offsets and
    frequency correction (over a wide range, specified as a HZ-independent
    fixed-point number) as needed. But that's a whole different
    discussion.

    That being said, it might be nice to do something about leap seconds.
    I always thought that the nanosecond count should include every
    possible leap second so that every time that actually happens
    corresponds to a unique count, but maybe that's just me.

    >> - Sub nanosecond field

    Me. A nanosecond is approximately a light-second. Other than things
    local to a single computer, not much of interest happens on a
    sub-nanosecond time scale. Also, a single 64-bit count is nice, and
    2^64 picoseconds isn't very long.

    >> - TAI time base (or according to parameter?)
    >
    > Having a CLOCK_TAI would be interesting across the board. We already
    > keep a TAI offset in the ntp code. However, I'm not sure if ntp actually
    > sets it these days.

    A friend of mine would probably appreciate various barycentric time
    scales as well. This would also be a different (and unrelated) patch.

    --Andy
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