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

[Michael S.Zick <mszick@goquest.com>]

On Saturday 26 July 2003 01:00 pm, Carlos O'Donell wrote:
> > If you map the page and make CPU 0 update the date, then I'll write the
> > userspace interface for gettimeofday.
> >
> > I'm not sure how we would do the check for 'do we see fast gettimeofday'
> > but it might be that we include a magic value there and check for it?
> > Other arches must have solved this.
>
> 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. 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. Could you explain the idea you have a bit
> more?
Note - some multiple cpu hardware intentionally clocks the cpu's at
slightly different rates to limit RFI generation.
Not sure if any HP-PARISC machines do such clocking.
Mike