On Wed, Jan 18, 2017 at 09:55:43AM -0200, Marcelo Tosatti wrote: > On Tue, Jan 10, 2017 at 05:36:48PM +0100, Paolo Bonzini wrote: > > > > > > On 05/01/2017 11:48, Marcelo Tosatti wrote: > > >> Host A has TSC scaling, host B doesn't have TSC scaling. We want > > >> to be able to start the VM on host A, and migrate to B. In this > > >> case, the only possible solution is to use B's frequency when > > >> starting the VM. The QEMU process doesn't have enough information > > >> to make that decision. > > > That is a good point. But again, its a special case and > > > should be supported by -cpu xxx,tsc-frequency=zzzz. > > > > I don't think this is a scenario that can work reliably. The computed > > TSC frequency may vary by 0.5% or so on every boot (e.g. you may get > > 2497000 kHz or 2511000 kHz for a 2.5 GHz TSC). You can start the VM on > > host A, reboot host B, and then you'll be unable to migrate. > > > > Paolo > > Including an acceptable error in the comparison seems to be > acceptable to work around that case. How much error is acceptable when exposing the invtsc flag to the guest? -- Eduardo -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
