Re: [libvirt] [PATCH v2 7/7] qemu: Check TSC frequency before starting QEMU

On Mon, Jun 03, 2019 at 02:27:58PM +0200, Jiri Denemark wrote: >When migrating a domain with invtsc CPU feature enabled, the TSC >frequency of the destination host must match the frequency used when the >domain was started on the source host or the destination host has to >support TSC scaling. > >If the frequencies do not match and the destination host does not >support TSC scaling, QEMU will fail to set the right TSC frequency when >starting vCPUs on the destination and thus migration will fail. However, >this is quite late since both host might have spent significant time >transferring memory and perhaps even storage data. > >By adding the check to libvirt we can let migration fail before any data >starts to be sent over. If for some reason libvirt is unable to detect >the host's TSC frequency or scaling support, we'll just let QEMU try and >the migration will either succeed or fail later. > >Luckily, we mandate TSC frequency to be explicitly set in the domain XML >to even allow migration of domains with invtsc. We can just check >whether the requested frequency is compatible with the current host >before starting QEMU. > >https://bugzilla.redhat.com/show_bug.cgi?id=1641702 > >Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; >--- > src/qemu/qemu_process.c | 53 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 53 insertions(+) > Reviewed-by: Ján Tomko <jtomko(a)redhat.com&gt;