On Fri, 2006-01-13 at 14:00 -0500, Lee Revell wrote:
> On Fri, 2006-01-13 at 10:56 -0800, Sven-Thorsten Dietrich wrote:
> > On Fri, 2006-01-13 at 10:55 -0800, [email protected] wrote:
> > > On Fri, Jan 13, 2006 at 01:09:51PM -0500, Lee Revell wrote:
> > > > > Some apps/users need higher resolution and lower overhead that only rdtsc
> > > > > can offer currently.
> > > >
> > > > But obviously if the TSC gives wildly inaccurate results, it cannot be
> > > > used no matter how low the overhead.
> > >
> > > unless we can re-sync the TSCs often enough that apps don't notice.
> > >
> >
> > You'd have to quantify that somehow, in terms of the max drift rate
> > (ppm), and the max resolution available (< tsc frequency).
> >
> > Either that, or track an offset, and use one TSC as truth, and update
> > the correction factor for the other TSCs as often as needed, maybe?
> >
> > This is kind of analogous to the "drift" NTP calculates against a
> > free-running oscillator.
> >
> > So you'd be pushing that functionality deeper into the OS-core.
> >
> > Dave Mills had that "hardpps" stuff in there for a while, it might be a
> > starting point.
> >
> > Just some thoughts for now...
> >
>
> It kind of makes you wonder what in the heck AMD were thinking, whether
> they realized that this design decision would cause so many problems at
> the OS level (it's broken at least Linux and Solaris). Maybe Windows
> keeps time in a way that was unaffected by this?
>
Last time I looked at Windows, we had to create an RT task to
interpolate between jiffies, b/c Windows was only keeping time at the
10 / 16 (smp) ms resolution. (to get NTP to run)
That was 6 years ago.
I haven't looked back since, and may I turn to salt or stone if I ever
do.
> Lee
>
--
***********************************
Sven-Thorsten Dietrich
Real-Time Software Architect
MontaVista Software, Inc.
1237 East Arques Ave.
Sunnyvale, CA 94085
Phone: 408.992.4515
Fax: 408.328.9204
http://www.mvista.com
Platform To Innovate
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