[lkml]   [2007]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: sparc generic time / clockevents
On Fri, 2007-02-23 at 16:34 -0800, David Miller wrote:
> From: john stultz <>
> Date: Fri, 23 Feb 2007 11:51:18 -0800
> > Yea. I actually have some in-progress patches from Peter Keilty that
> > convert ia64 and sparc64 time_interpolators to clocksources, then
> > removes the time_interpolator code.
> >
> > The ia64 conversion is more complicated due to the fsyscall asm, but I
> > think the sparc64 conversion (below) is pretty straight forward. I've
> > only built tested this, so I have no clue if it actually works.
> >
> > Any thoughts?
> Hey John, I had to do this already in order to do the dynticks
> port to sparc64, but nice to see another attempt :-)

Oh! Well, sorry for not sending it out earlier, then!

> Two things I did on my side:
> + .mask = 0xffffffffffffffffLL,
> I used CLOCKSOURCE_MASK(64) here.

Yep. That's better.

> +static cycle_t read_sparc64_cpuclock(void)
> +{
> + return (cycle_t)get_cycles();
> +}
> ...
> + .read = read_sparc64_cpuclock,
> You can just directly assign tick_ops->get_tick to .read at run-time
> to avoid a stack frame and function call/return.


> + .shift = 16,
> These shift selections all seem rather arbitrary.
> If it's not an arbitrary selection, it would be nice to have some
> comments about how to go about choosing an appropriate shift.
> I imagine the selections has to do with the possible range of
> the frequencies the clocksource supports, and how much
> accuracy you get for certain shift selections given that range.

Correct. The higher the shift value, the more precise NTP multiplier
adjustment we can make. However, too large w/ a high frequency
clocksource and you'll risk overflowing 64bits on the mult.

Although that's not super critical anymore since Roman implemented the
high-res error accounting, the net effect should be the same over the
long term(we just have to work harder w/ courser adjustments - resulting
in very small clock frequency oscillations).

I do need to get some documentation going. I had some back when I first
started pushing the changes, but so much was revised and rewritten it
stopped being correct.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-02-24 01:55    [from the cache]
©2003-2014 Jasper Spaans. hosted at Digital Ocean