* Marcelo Tosatti (mtosatti@xxxxxxxxxx) wrote: > On Mon, Nov 07, 2016 at 03:46:11PM +0000, Dr. David Alan Gilbert wrote: > > * Marcelo Tosatti (mtosatti@xxxxxxxxxx) wrote: > > > This patch, relative to pre-copy migration codepath, > > > measures the time between vm_stop() and pre_save(), > > > which includes copying the remaining RAM to destination, > > > and advances the clock by that amount. > > > > > > In a VM with 5 seconds downtime, this reduces the guest > > > clock difference on destination from 5s to 0.2s. > > > > > > Tested with Linux and Windows 2012 R2 guests with -cpu XXX,+hv-time. > > > > One thing that bothers me is that it's only this clock that's > > getting corrected; doesn't it cause things to get upset when > > one clock moves and the others dont? > > If you are correlating the clocks, then yes. > > Older Linux guests get upset (marking the TSC clocksource unstable > because the watchdog checks TSC vs kvmclock), but there is a workaround for it > in newer guests > (kvmclock interface to notify watchdog to not complain). > > Note marking TSC clocksource unstable on older guests is harmless > because kvmclock is the standard clocksource. > > For Windows guests, i don't know that Windows correlates between different > clocks. > > That is, there is relative control as to which software reads kvmclock > or Windows TIMER MSR, so i don't see the need to advance every clock > exposed. > > > Shouldn't the pause delay be recorded somewhere architecturally > > independent and then be a thing that kvm-clock happens to use and > > other clocks might as well? > > In theory, yes. In practice, i don't see the need for this... It seems unlikely to me that x86 is the only one that will want to do something similar. Dave -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- 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
