On Fri, Jan 06, 2017 at 08:31:27AM -0200, Marcelo Tosatti wrote: [...]
Maybe your use case just needs a explicit "invtsc-migration=on" command-line flag without a mechanism to abort migration on mismatch? I can't tell.
Again, there is no special case.
Note that even if we follow your suggestion and implement an alternative version of patch 4/4 to cover your use case, I will strongly recommend libvirt developers to support configuring TSC frequency if they want to support invtsc + migration without surprising/unpredictable restrictions on migratability.
Well, alright. If you make the TSC frequency of the host available to mgmt software as you describe, and write the steps mgmt software should take, i'm good.
I plan to. The problem is that the mechanism to query the host frequency may be unavailable in the first version.
Well just export KVM_GET_TSC_KHZ in a QMP command right? Its pretty easy.
Let me know if you need any help coding or testing.
I just found out that KVM doesn't provide something that QEMU and libvirt need: the value of kvm_max_guest_tsc_khz. Without it, we have no way to know if a given VM is really migratable to a host. Could we add a KVM_CAP_MAX_TSC_KHZ capability for that? -- Eduardo