DF as KVM Guest & Clock Skew - any experiences?

Sepherosa Ziehau sepherosa at gmail.com
Mon Oct 21 20:02:44 PDT 2013

On Tue, Oct 22, 2013 at 10:36 AM, Chris Turner <c.turner at 199technologies.com
> wrote:

> Hello -
> Trying to run a 64bit DF guest on F18, am getting
> some odd clock jitter both with and without dntpd
> running from the guest, and needless to say, 'make'
> doesn't like this.

What's the output of
sysctl kern.cputimer

There are several cputimers.  You could disable them through tunables
hw.tsc_cputimer_enable="0" (disable TSC cputimer, enabled by default)
debug.acpi.disabled="hpet timer" (disable HPET and ACPI cputimer, enabled
by default)

If they are all enabled (default) and are all functional, their priority
relationship is TSC > HPET > ACPI

If they are all disabled, the only one left is i8254.

Best Regards,

> I seem to recall having similar issues with DF-on-DF
> QEMU on dragonfly, and my 'fix' was to noodle with
> the emulated time source on QEMU, falling back to a low
> resolution clock source (e.g. RTC instead of HPET)
> that the emulator could more deterministically provide,
> allowing clock calibration to be less sensitive,
> and the system to run without much significant clock
> jitter..
> However, I'm not seeing any clear signs that
> the libvirt/KVM stuff allows this level of noodling,
> though I admittedly haven't done an exhaustive search.
> Anyone have any experiences / fixes here?
> Cheers,
> - Chris

Tomorrow Will Never Die
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