On 05/01/2017 14:00, Daniel P. Berrange wrote: >> If you do this unconditionally, you have another problem: if >> tsc-frequency is set explicitly, migration is only possible if >> TSC frequency of the destination matches[1], or if TSC scaling is >> supported by the destination. It's a good idea to set a TSC >> frequency only if invtsc is enabled explicitly in the config. > > If we don't set tsc-frequency and the TSC frequency doesn't > match, does that mean the guest migration succeed, but suddenly > sees different TSC frequency ?
That's the reason why kvmclock exists (or more precisely, the reason why kvmclock is still useful even when hosts have invtsc). Paolo > I guess we we allowed that historically we can't break that > now, so setting it only if invtsc is set seems reasonable.
