[libvirt] [RFC] kvm: x86: export vCPU halted state to sysfs

[Luiz Capitulino]

On Fri, 2 Feb 2018 15:54:15 +0000
Daniel P. Berrangé <berrange at redhat.com> wrote:

> > > The most important question I have is: does this solution satisfy the
> > > needs of upper management? That is, if we implement the solution suggested
> > > by Eduardo than the feature of automatically hotplugging more CPUs
> > > will only work for s390. Is this OK?
> > > 
> > > If yes, then I think this is the best solution. And the next question
> > > would be: Viktor, can you change this in libvirt while we fix query-cpus
> > > in QEMU?
> > >   
> > The latest proposal was to use a flag for query-cpus (like full-state)
> > which would control the set of properties queried and reported. If this
> > is the way we decide to go, I can make the necessary changes in libvirt.  
> 
> Regardless of whether we add that flag to query-cpus or not, we still have
> the general problem of solving the cross-architecture semantics to be
> more sane.

Let's the both then:

 o Make qemuDomainRefreshVcpuHalted() s390-only in libvirt. This by
   itself fixes the original performance issue

 o Deprecate the "halted" field in query-cpus in QEMU. This fixes new
   instances of this same problem