On 02/02/2018 08:50 AM, 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 <berra...@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?
Removing an output field outright may break a client that depended on the field; so a deprecation period is definitely required there. But it is okay, documentation-wise, to state that a field is output always as 0 for back-compatibility reasons and that modern clients should ignore it (which would then let old clients still parse the field, but no longer see a non-zero value), whether or not we also pursue the deprecation course and eventually remove the field after more releases. See CpuInfo::current, for an example. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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