On Fri, 2006-02-17 at 11:43 +1100, Paul Mackerras wrote:
> john stultz writes:
>
> > > + if (time_adjust_step)
> > > /* Reduce by this step the amount of time left */
> > > time_adjust -= time_adjust_step;
> >
> > Does the if statement really buy you anything here?
>
> Well, just avoiding dirtying a cache line in the common case where
> time_adjust and time_adjust_step are zero, that's all. It's a very
> minor thing. In fact if time_adjust is zero we could avoid the
> procedure call, the subtraction and the multiplication by 1000, like
> this:
>
> delta_nsec = tick_nsec;
> if (time_adjust) {
> time_adjust_step = adjtime_adjustment();
> /* Reduce by this step the amount of time left */
> time_adjust -= time_adjust_step;
> delta_nsec += time_adjust_step * 1000;
> }
Yea, I was thinking if you weren't going to do it for the mult, why
bother on the subtract. Either way, I'm not too picky, it should just be
consistent.
> > > +u64 current_tick_length(void)
> > > +{
> > > + long delta_nsec;
> > > +
> > > + delta_nsec = tick_nsec + adjtime_adjustment() * 1000;
> > > + return ((u64) delta_nsec << (SHIFT_SCALE - 10)) + time_adj;
> > > +}
> >
> > You've got time_adj here, but you're not using what's been accumulated
> > in time_phase, is that really ok?
>
> Yes.
>
> What's been accumulated in time_phase is always less than a
> nanosecond's worth. I took the approach of delivering the full
> precision of time_adj to the arch code (i.e. including the 12 bits to
> the right of the binary point), rather than truncating it to whole
> nanoseconds and then having to vary it by +/- 1 nanosecond each tick.
So you're accumulating it yourself in the arch code? That's fine, I just
wanted to be sure.
Acked-by: john stultz <[email protected]>
thanks
-john
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