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.