2016-02-24 21:53+0100, Radim Krčmář: > 2016-02-24 12:24-0800, Andy Lutomirski: >> On Wed, Feb 24, 2016 at 12:17 PM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: >>> Do you find anything incorrect with >>> * kvmclock measures the flow of time. >>> * time in kvmclock flows at the same rate as host's CLOCK_BOOTTIME. >>> ? >> >> If we could supply CLOCK_REALTIME as well and advertise that fact to >> guest userspace (perhaps with a sysctl or similar in the guest to turn >> it on), it would be *awesome*. Guests with access to this feature >> could simply not run ntpd/chronyd. > > I think that pvclock_wall_clock interface is there to do that. > (If pvclock_vcpu_time_info can provide what is claimed above.) > > If pvclock_wall_clock version field matches with pvclock_vcpu_time_info, Correction: versioning schemes are independent. (pvclock_wall_clock needs a version because of CPUs that can't atomically access 64 bits.) > then the guest can add those two and get CLOCK_REALTIME. pvclock_wall_clock provides CLOCK_REALTIME when pvclock_wall_clock was 0, so the guest can just add them to get current CLOCK_REALTIME. (The agreement is that CLOCK_REALTIME started in 1970.) -- 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
