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

[Peter Krempa]

On 04/09/13 15:06, Luiz Capitulino wrote:
> On Mon, 08 Apr 2013 11:14:32 -0600
> Eric Blake <address@hidden> 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 <address@hidden>
> > > ---
> > >   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 <address@hidden>