Re: [Qemu-devel] [PATCHv3 2/4] qmp: add query-cpus-fast

[Eric Blake <eblake@redhat.com>]

On 02/15/2018 08:40 AM, Viktor Mihajlovski wrote:
> On 15.02.2018 15:19, Eric Blake wrote:
>> On 02/15/2018 04:20 AM, Viktor Mihajlovski wrote:
>>> From: Luiz Capitulino <lcapitulino@redhat.com>
>>>
>>> The query-cpus command has an extremely serious side effect:
>>> it always interrupts all running vCPUs so that they can run
>>> ioctl calls. This can cause a huge performance degradation for
>>> some workloads. And most of the information retrieved by the
>>> ioctl calls are not even used by query-cpus.
>>>
>>> This commit introduces a replacement for query-cpus called

>> You know, we have no back-compat guarantees on HMP.  We could make 'info
>> cpu' just ALWAYS call query-cpus-fast, with no HMP counterpart for the
>> slower query-cpus, and without needing a deprecation period.  But I'll
>> leave that up to David if that makes more sense.
> Ditching info cpus_fast would make me happy as well, because it would
> cause less headache on the libvirt side of things.

Why is libvirt using HMP in the first place?  Libvirt should always be 
using the QMP command, when one exists.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org