Re: [Qemu-devel] [PATCH v2] New cpu-max field in query-machines QMP command output

[Peter Krempa <pkrempa@redhat.com>]

On 04/09/13 15:06, Luiz Capitulino wrote:
> On Mon, 08 Apr 2013 11:14:32 -0600
> Eric Blake <eblake@redhat.com> wrote:
>
>> On 04/08/2013 10:41 AM, Michal Novotny wrote:
>>> Alter the query-machines QMP command to output information about
>>> maximum number of CPUs for each machine type with default value
>>> set to 1 in case the number of max_cpus is not set.
>>>
>>> Signed-off-by: Michal Novotny <minovotn@redhat.com>
>>> ---
>>>   qapi-schema.json | 4 +++-
>>>   vl.c             | 1 +
>>>   2 files changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/qapi-schema.json b/qapi-schema.json
>>> index db542f6..689ca8d 100644
>>> --- a/qapi-schema.json
>>> +++ b/qapi-schema.json
>>> @@ -2861,11 +2861,13 @@
>>>   #
>>>   # @default: #optional whether the machine is default
>>>   #
>>> +# @cpu-max: maximum number of CPUs supported by the machine type
>>
>> Typically, when adding a field in a later version than the original
>> introduction of the datatype, we add '(since 1.5)' to make it obvious
>> when to expect the field.  However, as nothing (currently) enforces this
>> rule, I think such an addition is minor enough that it wouldn't
>> invalidate the use of my:
>
> Oh, it turns out I was making some confusion with this patch and
> didn't realize it was extending the query-machines command.
>
> I don't mean there's anything wrong with it, but my question is: doesn't
> this patch invalidates query-cpu-max?

Unfortunately, for libvirt query-cpu-max isn't really usable as it needs 
us to start qemu with the correct machine type. This would increase 
overhead as we would need to start the qemu process with a safe number 
of cpus, use query-cpu-max and then restart the process.

The information added in the query-machines output can on the other hand 
be cached (we are already doing this for the machine types) and used 
later from the cache without increasing overhead.

So yes, I think it invalidates query-cpu-max and it can be removed in 
case it wasn't released.

Peter

>
> PS: I can add the '(since 1.5)' line myself.
>
>>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
>>
>
>