Question about migration of a VM between hosts having slight difference in TSC Frequency

[Veselina Radeva]

Hi,

I'm trying to migrate a VM from one host to another where there is a 1KHz difference in the TSC frequency between hosts. This results in errors caused by this warning, so migration fails. On the other hand, I can see few lines before that that there is a try to allow TSC frequency difference between host and VM if it falls within the specified bounds. It seems like `KVM_SET_TSC_KHZ`succeeds only when TSC Scaling is available. Practically this means that migration between hosts having difference in TSC frequency, even when it falls within bounds, is possible only when TSC scaling is available. 

On the other hand, in libvirt, migration is allowed if TSC frequency difference falls within bounds, no matter if TSC scaling is enabled or not.

So, I was wondering is it intended not to allow migration between hosts having differences in TSC frequency if TSC scaling is not available? Or is it a bug?

Thanks in advance,

Veselina Radeva

https://st6.io/