On Sat, Oct 7, 2017 at 5:52 PM, Adam Steen <[email protected]> wrote:
> On Fri, Oct 06, 2017 at 03:58:18PM +0200, Mike Belopuhov wrote:
> > Hi,
> >
> > An experimental change to use TSC as a timecounter source on a variety
> > of modern Intel and AMD CPUs has been just committed and enabled on
> > OpenBSD/amd64 thanks to the work done by Adam Steen.
> >
> > The rationale is, quoting the commit message:
> >
> > If frequency of an invariant (non-stop) time stamp counter is measured
> > using an independent working timecounter that has a known frequency, we
> > can assume that the measured TSC frequency is as good as the resolution
> > of the timecounter that we use to perform the measurement. This lets us
> > switch from this high quality but expensive source to the cheaper TSC
> > without sacrificing precision on a wide range of modern CPUs.
> >
> > You can query and change the current timecounter source in the runtime
> > via sysctl:
> >
> > % sysctl kern.timecounter.{choice,hardware}
> > kern.timecounter.choice=i8254(0) tsc(2000) acpihpet0(1000)
> acpitimer0(1000) dummy(-1000000)
> > kern.timecounter.hardware=tsc
> >
> > Please make sure your NTP drift (/var/db/ntpd.drift) stays within
> -20..+20
> > or at least is not worse than it is right now.
> >
> > And finally, please make sure to run a "make config" when building the
> > kernel to update offset tables because of the cpu_info structure changes.
> >
> > Regards,
> > Mike
> >
>
> Hi,
>
> Now that we have an accurate tsc frequency, I would like to expose this
> information to userland via a sysctl.
>
> The diff below exposes the tsc frequency and if it is invariant.
>
> Cheers,
> Adam
>
>
Please ignore that diff, looks like i had some dregs from a older diff i
had been testing
