Open Stack

On Fri, Sep 26, 2014 at 01:03:06PM -0400, Sean Toner wrote:
> On Friday, September 26, 2014 03:09:05 PM Daniel P. Berrange wrote:
> 
> > > 1. What happens on an overcommit for the number of guest CPUs?
> > > 
> > >    - For example, if I have a system with 2 sockets 4 cores each,
> > >    what
> > > 
> > > would happen if I have 2 guests, each one wanting 6 cores (assuming
> > > this is not in violation of the hw:cpu_max_cores)?
> > > 2. What happens on an overcommit on memory?
> > 
> > The memory and CPU overcommit settings are still honoured when Nova
> > does NUMA placement. eg if you have a host with 2 NUMA nodes, each
> > with 4 physical CPUs and CPU overcommit ratio of x3, then Nova will
> > treat this as being a system with 2 NUMA nodes, each with 12 CPUs.
> > Similarly for memory overcommit.
> > 
> 
> So in the scenario you describe above, each guest configuration would be 
> constrained to one NUMA node (since the NUMA node would present itself 
> logically as having 12 CPUs)?  

No, the overcommit ratio is only used when considered the overall load
of the system. When deciding whether a guest can fit on a NUMA node, it
still uses the actual hardware count. So if a node has 4 CPUs, then a
6 CPU guest will be spread across 2 nodes perhaps 3 CPUs on each node.
So with overcommit you could run 4 copies of the guest before the nodes
were full according to overcommit ratio.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|