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

[Jiri Denemark]

On Mon, Jun 03, 2019 at 14:52:40 +0200, Ján Tomko wrote:
> 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 at redhat.com>
> >---
> > src/qemu/qemu_process.c | 53 +++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 53 insertions(+)
> >
> 
> Reviewed-by: Ján Tomko <jtomko at redhat.com>

Thanks for the review and I'm sorry for forgetting to add the
Reviewed-by line into the commits before pushing.

Jirka