On Mon, Apr 18, 2011 at 08:02:35PM -0400, Zachary Amsden wrote:
> >
> > On Sat, Apr 16, 2011 at 06:09:17PM +0200, Jan Kiszka wrote:
> >
> >> On 2011-03-25 09:44, Joerg Roedel wrote:
> >>
> >
> >>> + tsc_delta = !vcpu->arch.last_guest_tsc ? 0 :
> >>> + tsc - vcpu->arch.last_guest_tsc;
> >>>
> >
> >> This patch appears to cause troubles to Linux guests on TSC clocksource
> >> and APIC highres timer. The first boot after qemu start is always fine,
> >> but after a reboot the guest timer appears to fire incorrectly or even
> >> not at all.
> >>
> >> Was this patch tested with a guest reboot scenario as well? Does it
> >> account for the TSC being reset to 0 on reboot?
> >>
> > Hmm, probably the last_guest_tsc is not updated correctly in this
> > scenario. I will have a look tomorrow.
> >
> > Joerg
> >
> >
>
> To avoid this problem, when the TSC is reset, the overshoot protection
> where last_guest_tsc is used is specifically disabled:
>
> /* Reset of TSC must disable overshoot protection below */
> vcpu->arch.hv_clock.tsc_timestamp = 0;
> vcpu->arch.last_tsc_write = data;
> vcpu->arch.last_tsc_nsec = ns;
>
> You can probably use the same test - last_guest_tsc is only valid if
> tsc_timestamp above != 0.
Yes, this should also work. But the other way we get rid of
last_host_tsc which is also a good thing :)
Joerg
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