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    SubjectRe: + stupid-hack-to-make-mainline-build.patch added to -mm tree
    On 03/06/2007 05:18 PM, Thomas Gleixner wrote:
    > On Tue, 2007-03-06 at 16:53 -0800, Dan Hecht wrote:
    >>> Ooops. I completely forgot, that you get the absolute expiry time
    >>> already in ktime_t format (nanoseconds) when dev->set_next_event() is
    >>> called.
    >>>
    >>> dev->next_event = expires;
    >>>
    >>> is done right before the call.
    >>>
    >>> So it's already there for free.
    >>>
    >>>
    >> Okay. I noticed that but didn't think it was okay to use since it
    >> didn't seem like it was set up for the clock_event_device code's use, so
    >> seemed like a conceptual interface violation to go digging around in
    >> there.
    >
    > Yes it is.
    >
    > I just wanted to point out that you can use it until I'm awake enough to
    > implement it proper.
    >

    Well, we'll probably just live with using the relative expiry for the
    first pass, and then revisit this later once that is working, rather
    than resort to hacking it out by reading ->next_event.

    >> Also, wasn't one of the points of clockevents to prevent the device code
    >> from doing conversions between nanoseconds and clicks themselves? Don't
    >> we really want the clockevents generic layer to do this conversion
    >> between monotonic nanonseconds to absolute device clicks and then give
    >> the device code that value, so the device layer doesn't perform any
    >> conversions?
    >
    > Right. But this applies only to deltas, as the conversion of absolute
    > time values gets ugly, i.e. 128bit math
    >

    Yeah, hopefully we can come up with a clean way to do this. But, like I
    said early, until we do, we'll stick with the relative expiry.

    > IMO the paravirt interfaces should use nanoseconds anyway for both
    > readout and next event programming. That way the conversion is done in
    > the hypervisor once and the clocksources and clockevents are simple and
    > unified (except for the underlying hypervisor calls).
    >

    I disagree. The clocksource/clockevents layer are always going to have
    to convert nanoseconds to/from hardware units, so why not use it? And,
    some guests (say, a future version of linux that does trace-based
    process accounting) may want higher resolution than nanoseconds for
    certain uses. In any case, this is beside the point; I'd prefer to
    stick to using the clockevents interface in the way it was intended
    rather than reaching into ->next_event.

    thanks,
    Dan
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