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> 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.
Regards,
Daniel
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