[Kimchi-devel] RFC: smt support

[Christy Perez]

On Wed, 2014-07-02 at 09:50 -0300, Paulo Ricardo Paz Vital wrote:
> > 
> > On 07/01/2014 11:32 PM, Aline Manera wrote:
> > >
> > > On 06/26/2014 07:27 PM, Christy Perez wrote:
> > >> Quick poll for adding support for
> > >> <cpu>
> > >>      <topology sockets='1' cores='2' threads='1'/>
> > >> </cpu>
> > >>
> > >> I know it would be nice to let users add it on a per-vm basis, but maybe
> > >> it might be something that we'd rather just leave in the template only.
> > >> Having it in the template only seems simpler when thinking about UI
> > >> design, imo, but I'd love to hear what everyone else thinks.
> > >
> > > According to the reference 
> > > https://www.ibm.com/developerworks/community/blogs/fe313521-2e95-46f2-817d-44a4f27eba32/entry/enabling_smt_on_powerkvm_guests?lang=en
> > >
> > > There are some restrictions to configure SMT what can not be intuitive 
> > > for a Kimchi user.
> > >
> > > So I like the idea to keep it only on templates (at least for while) 
> > > and see how Kimchi users react on that.
> > > We will need to properly add a logic to get the best pairs of 
> > > cores/threads according to the vcpus number.
> > >
> > > In my mind, we should only add a check box on Template edit: "Enable 
> > > SMT" if checked Kimchi knows what it needs to do when creating a VM
> > >
I'm fine with only on template edit. In the future, though, hopefully
we'll be adding maybe an "Advanced" sub-panel when creating templates
that lets users do things like this?
> 
> I think we can do something better! In addition to the check box, we can
> provide a combo box with the available choices for SMT. These values are
> static defined as SMT=1, SMT=2, SMT=4, or SMT=8. 
> 
> So, when the user select the SMT check box, the combo box make enable to
> user select one of these 4 options. Then, at the moment to write the
> XML, Kimchi backend do math to create the topology entry based on the
> SMT value and the number of processors defined.
> 
> For example, if user sets a template to have 8 processors and SMT=4, the
> backend must create following entry on the XML file:
> 
What if they set 7 processors? We could disable the SMT checkboxes if
their CPU # wasn't a multiple of anything. So we'll probably have to
come up with very good help/hint text for this. 

Or, if they select SMT, the CPU box becomes un-editable, and then
selecting one of the SMT options, the CPU count (in the un-editable
field) is updated so that they can understand what VCPU count they'll
end up before they click OK.

> <vcpu>8</vcpu>
> <cpu>
> <topology sockets='1' cores='2' threads='4'/>
> </cpu>  
> 
> That's my 3 cents.
> Thanks and best regards,
> Paulo Vital
>