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 -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
