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

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

On 15.02.2018 15:53, Eric Blake wrote:
> 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.
> Which it does, but there's still a lot of fallback code including HMP
"info cpus". In real life this should of course never be used, because
the QMP is always there.

-- 
Regards,
 Viktor Mihajlovski