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

[Matthew Wilcox <willy@debian.org>]

On Mon, Jul 28, 2003 at 11:57:04AM -0400, Carlos O'Donell wrote:
> > Yes we can. We can sync CR16 across CPUs within a few CPU cycles.
> > I've described this before on parisc-linux.
> 
> It might be too costly to do the sync'ing all the time, and too costly
> for a fast gettimeofday to do a sync at the polling point.
>  
> > 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().
> 
> 
> The whole point behind fast gettimeofday is that userspace apps that
> want to do timestamping on a _very_ accurate granularity (e.g.
> nanosecondes) can get monotically incrementing numbers on each
> gettimeofday. Do we even have such a fast clock on PA? What is the
> fastest clock across the most boxes?

You know, you don't even need kernel help for this.  According to page
2-5 of the Kane book, the Interval Timer is accessible by non-privileged
instructions.

-- 
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