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    SubjectRe: [PATCH 01/13] hrtimer: round up relative start time

    * Roman Zippel <> wrote:

    > Hi,
    > On Mon, 13 Feb 2006, Ingo Molnar wrote:
    > > but there is no 'old behavior' to restore to. The +1 to itimer intervals
    > > caused artifacts that were hitting users and caused 2.4 -> 2.6 itimer
    > > regressions, which hrtimers fixed. E.g.:
    > >
    > >
    > Ingo, please read correctly, this is mainly about interval timers,
    > which my patch doesn't change. My patch only fixes the initial start
    > time.

    Yeah, i know it's about the start time - what else could it possibly be
    about? As i wrote:

    > > so i dont think restoring the first timeout of an interval timer to
    > > be increased by resolution [which your patch does] has any meaning.
    > > It 'restores' to half of what 2.6 did prior hrtimers. Doing that
    > > would be inconsistent and would push the 'sum-up' errors observed
    > > for interval timers above to be again observable in user-space (if
    > > user-space does a series of timeouts). What's the point?

    Your change changes the initial start time to be longer by +1 jiffy. My
    "restores to half of what 2.6 did" observation was in reference to the
    start time. The other half is the interval time between timeouts. If you
    add a +1 jiffy to the start time, you ought to do it for the interval
    time too. Or do it for neither - which is what we chose to do.

    Yes, the 2.6 regression in the bugzilla was _mainly_ about the intervals
    adding a comulative +1, but obviously the behavior should be symmetric:
    if we use our higher resolution for intervals, we should use it for the
    start time too.

    In other words: your patch re-introduces half of the bug on low-res
    platforms. Users doing a series of one-shot itimer calls would be
    exposed to the same kind of (incorrect and unnecessary) summing-up
    errors. What's the point?

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