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    SubjectRe: [PATCH] [RFC] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes
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    On Thu, 2010-12-02 at 01:18 +0000, Jamie Lokier wrote:
    > Valdis.Kletnieks@vt.edu wrote:
    > > On Wed, 01 Dec 2010 10:43:59 GMT, Jamie Lokier said:
    > >
    > > > So maybe CLOCK_MONOTONIC should be changed to include elapsed time
    > > > during suspend/resume, and CLOCK_MONOTONIC_RAW could remain as it is,
    > > > for programs that want that?
    > >
    > > Wouldn't that be an API break for programs that are expecting the current
    > > behavior of CLOCK_MONOTONIC? Yes, there should be a way to request either of
    > > them - but if there's only one way now, it should continue to act the current
    > > way, and the added way is the second option.
    >
    > I don't know. Can you think of any program which would break if
    > suspend/resume's clocks behaved like ordinary task scheduling - when a
    > task doesn't run for a long time because of scheduling decisions?
    > Hmm, I guess some realtime apps might like to know.

    Like I mentioned earlier, CLOCK_MONOTONIC_RAW and CLOCK_MONOTONIC are
    tightly tied, so anything using CLOCK_MONOTONIC_RAW would break.

    It might be possible to change both, but I still think such a change
    would be bad.

    > Currently CLOCK_MONOTONIC jumps forwards by 4 seconds on
    > suspend/resume anyway (as seen by userspace), on my x86 laptop running
    > 2.6.37-rc3. So it does already jump a bit...

    So just to clarify here, by this do you mean that there's ~4 seconds
    delay between the resume event and when userland apps start to run (or
    possibly some of that accumulating between the app freeze and the
    timekeeping suspend) ?

    Or are you seeing CLOCK_MONOTONIC jump 4 seconds out of sync with
    CLOCK_REALTIME?

    It should be the delta between CLOCK_MONOTONIC and CLOCK_REALTIME prior
    to suspend should be that same delta + suspend time after resume. If
    that's not the case, something may be broken.

    thanks
    -john



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