[Libvir] Extending libvirt to probe NUMA topology

[Ryan Harper]

* Richard W.M. Jones <rjones at redhat.com> [2007-09-06 09:45]:
> Daniel Veillard wrote:
> >1) Provide a function describing the topology as an XML instance:
> >
> >   char *	virNodeGetTopology(virConnectPtr conn);
> 
> >which would return an XML instance as in virConnectGetCapabilities. I
> >toyed with the idea of extending virConnectGetCapabilities() to add a
> >topology section in case of NUMA support at the hypervisor level, but
> >it was looking to me that the two might be used at different times
> >and separating both might be a bit cleaner, but I could be convinced
> >otherwise.
> 
> I'd definitely prefer to extend virConnectGetCapabilities XML.  It 
> avoids changing the remote driver and language bindings, and really 
> callers only need to pull capabilities once per connection.
> 
> >---------------------------------
> ><topology>
> >  <cells num='2'>
> >    <cell id='0'>
> >      <cpus num='2'>
> >        <cpu id='0'/>
> >        <cpu id='1'/>
> >      </cpus>
> >      <memory size='2097152'/>
> >    </cell>
> >    <cell id='1'>
> >      <cpus num='2'>
> >        <cpu id='2'/>
> >        <cpu id='3'/>
> >      </cpus>
> >      <memory size='2097152'/>
> >    </cell>
> >  </cells>
> ></topology>
> >---------------------------------
> >
> >  A few things to note:
> >   - the <cells> element list the top sibling cells
> 
> Not <nodes>?
> 
> >   - the <cell> element describes as child the resources available
> >     like the list of CPUs, the size of the local memory, that could
> >     be extended by disk descriptions too
> >     <disk dev='/dev/sdb'/>
> >     and possibly other special devices (no idea what ATM).
> >
> >   - in case of deeper hierarchical topology one may need to be able to
> >     name sub-cells and the format could be extended for example as
> >     <cells num='2'>
> >       <cells num='2'>
> >         <cell id='1'>
> >           ...
> >         </cell>
> >         <cell id='2'>
> >           ...
> >         </cell>
> >       </cells>
> >       <cells num='2'>
> >         <cell id='3'>
> >           ...
> >         </cell>
> >         <cell id='4'>
> >           ...
> >         </cell>
> >       </cells>
> >     </cells>
> >     But that can be discussed/changed when the need arise :-)
> 
> Especially note that 4 (or more) socket AMDs have a topology like this, 
> with two different penalties for reaching nodes which are one and two 
> hops away.  Do we have a way to describe the penalties along different 
> paths?

The SLIT table provides distance cost values.  Xen isn't messing with
SLIT information at the moment.  I'm not sure about Linux or Sun, but I
would expect that they would.


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh at us.ibm.com