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

[Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>]

On 02.02.2018 21:41, Eduardo Habkost wrote:
> On Fri, Feb 02, 2018 at 03:19:45PM -0500, Luiz Capitulino wrote:
>> On Fri, 2 Feb 2018 18:09:12 -0200
>> Eduardo Habkost <ehabkost@redhat.com> wrote:
> [...]
>>> Your plan above covers what will happen when using newer QEMU
>>> versions, but libvirt still needs to work sanely if running QEMU
>>> 2.11.  My suggestion is that libvirt do not run query-cpus to ask
>>> for the "halted" field on any architecture except s390.
>>
>> My current plan is to ask libvirt to completely remove query-cpus
>> usage, independent of the arch and use the new command instead.
> 
> This would be a regression for people running QEMU 2.11 on s390.
> 
> (But maybe it would be an acceptable regression?  Viktor, what do
> you think?  Are there production releases of management systems
> that already rely on vcpu.<n>.halted?)
> 
Unfortunately, there's code out there looking at vcpu.<n>.halted. I've
informed the product team about the issue.

If we drop/deprecate vcpu.<n>.halted from the domain statistics, this
should be done for all arches, if there's a replacement mechanism (i.e.
new VCPU states). As a stop-gap measure we can make the call
arch-dependent until the new stuff is in place.

BTW: libvirt cannot eliminate query-cpus entirely because initial CPU
topology and changes due to hotplug must be queried.

-- 
Regards,
 Viktor Mihajlovski