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SubjectRe: [RFC][PATCH] new timeofday arch specific hooks (v. A2)

On Wed, 26 Jan 2005, Benjamin Herrenschmidt wrote:

> On Tue, 2005-01-25 at 16:34 -0800, Christoph Lameter wrote:
>
> > I just hope that the implementation of one arch does not become a standard
> > without sufficient reflection. Could we first get an explanation of
> > the rationale of the offsets? From my viewpoint of the ia64 implementation
> > I have some difficulty understanding why such complicated things as
> > prescale and postscale are necessary in gettimeday and why the simple
> > formula that we use in gettimeofday is not sufficient?
>
> What is complicated here ? The formula, at least as we do on ppc64, is
> simply:
>
> time = (hw_value - prescale offset) / scale + post scale offset

Yes that is basically what we do on ia64 but we use different
terminology.

time = ns_at_last_tick + (hw_value - last_tick_hw_value) * scale >> shift

> > What I think is a priority need is some subsystem that manages
> > time sources effectively (including the ability of the ntp code to
> > scale the appropriately) and does that in an arch independent
> > way so that all the code can be consolidated. Extract the best existing
> > solutions and work from there.
>
> Which is what John is trying to do, so help instead of criticizing :)

I sure hope that we will be doing that. But so far this has been
a new implementation instead otherwise ntp_scale would not be in the
gettimeofday function.
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