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Re: [Libvir] [RFC][PATCH 1/2] Tested NUMA patches for available memory and topology



On Fri, Sep 28, 2007 at 03:45:31PM +0100, Daniel P. Berrange wrote:
> On Fri, Sep 28, 2007 at 02:52:51PM +0100, Richard W.M. Jones wrote:
> > # src/virsh capabilities
> > [...]
> >   <topology>
> >     <cells num='1'>
> >       <cell id='0'>
> >         <cpus num='4'>
> >            <cpu id='0'/>
> >            <cpu id='1'/>
> >            <cpu id='2'/>
> >            <cpu id='3'/>
> >         </cpus>
> >       </cell>
> >     </cells>
> >   </topology>
> 
> Do we really need such verbose XML. At the very least the 'num' attribute
> is redundant, since you can trivially do count(/topology/cells/cell) or
> count(/topology/cells/cell[ id=0]/cpus/cpu) XPath exprs in both cases.
> 
> The addition of extra tags every time we have a list is not the style we
> have normally used in libvirt. eg, we don't use
> 
>     <disks>
>        <disk>
>           ..
>        </disk>
>        <disk>
>           ..
>        </disk>
>     </disk>
> 
> to surround the list of disks in a domain.
> 
> I'd prefer to see it looking more like this:
> 
>    <topology>
>      <cell id='0'> 
>        <cpu id='0'/>
>        <cpu id='1'/>
>        <cpu id='2'/>
>        <cpu id='3'/>
>      </cell>
>    </topology>

  I explained why I preferred a more structured approach and the <cells>
construction when I made the proposal
  https://www.redhat.com/archives/libvir-list/2007-September/msg00015.html
basically you may hit hierachical topologies which are not flat.
If you want to remove the nums= that mean that from an user perspective if
you use a streaming interface (like SAX) you can't know a priori the size
of the arrays you need to allocate to fill the information. I prefer something
a bit more verbose and a bit more complex to generate but more flexible
in its use. For me <cells> can't go away for structural needs and the count
is for the number of children at that level not at all levels.
  We could get rid of <cpus> but 
    <cpus num='4'>
      <cpu id='0'/>
      <cpu id='1'/>
      <cpu id='3'/>
    </cpus>
could allow things like description in hotplug CPUs situations where the
structure/topology does not change but the content does.

Since that part is rather experimental, I prefer to have more structure 
than what may looks like sticly necessary right now but have provisions
for the future.

Daniel

-- 
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/


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