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

On Fri, Feb 02, 2018 at 12:50:14PM -0200, Eduardo Habkost wrote: > (CCing qemu-devel) > > On Fri, Feb 02, 2018 at 09:21:59AM -0500, Luiz Capitulino wrote: > > On Fri, 2 Feb 2018 14:19:38 +0000 > > Daniel P. Berrangé <berrange(a)redhat.com&gt; wrote: > > > On Fri, Feb 02, 2018 at 12:15:54PM -0200, Eduardo Habkost wrote: > [...] > > > > It would be also interesting to update QEMU QMP documentation to > > > > clarify the arch-specific semantics of "halted". > > > > > > Any also especially clarify the awful performance implications of running > > > this particular query command. In general I would not expect query-xxx > > > monitor commands to interrupt all vcpus, so we should clearly warn about > > > this ! > > > > Or deprecate it... > > We could deprecate the expensive fields on query-cpus, and move > them to a more expensive query-cpu-state command. I believe most > users of query-cpus are only interested in qom_path, thread_id, > and topology info. > > Markus, Eric: from the QAPI point of view, is it OK to remove > fields between QEMU versions, as long as we follow our > deprecation policy? I would expect that to not be OK. A fully backwards compatible way to deal with this would just be to add a flag to the query-cpus command eg something like query-cpus arch-specific=false to turn off all this arch specific state, and just report the cheap generic info. If it defaults to arch-specific=true when omitted, then there's no compat problems.