Re: [parisc-linux] Generic light-weight syscall.

[Grant Grundler <grundler@parisc-linux.org>]

On Sat, Jul 26, 2003 at 02:00:32PM -0400, Carlos O'Donell wrote:
> Talked to Rik Van Riel about fast gettimeofday and he indicated that
> it's not doable since you can't guarantee your process will get
> scheduled on another CPU whose clock is out of sync by more than X and
> get negative time.

Yes we can. We can sync CR16 across CPUs within a few CPU cycles.
I've described this before on parisc-linux.

"sync" means figure out the difference between CR16 on several
CPUs and using CPU 0 as the reference.

> Though I imagine you were talking about having one
> CPU update one page with time on it... and then other CPU's read this?
> LaMont notes that there is no requirement from the PA design that CPU's
> clock at _exactly_ the same frequency or have monotonically incrementing
> clocks at the right rate.

correct. IIRC 9000/870 have seperate clock sources.
But all the boxes we support to date have exactly one clock source.
The multi-cell boxes (like superdome) will have multiple sources
and I don't know how to handle those - maybe a "not quite so fast"
gettimeofday().

hth,
grant