[libvirt] [Xen-devel] libvirt/libxl implemetation of get_online_cpu / virNodeGetCPUMap?

[Ian Campbell]

On Wed, 2015-02-25 at 15:20 +0000, Daniel P. Berrange wrote:
> On Wed, Feb 25, 2015 at 03:13:36PM +0000, Ian Campbell wrote:
> > On Wed, 2015-02-25 at 15:03 +0000, Daniel P. Berrange wrote:
> > > FWIW, this code in openstack was only added for benefit of s390
> > > architecture where apparently it is common to have hosts with
> > > CPUs offlined. Presumably you have to pay IBM for each extra
> > > CPU you turn online :)
> > 
> > Presumably :-)
> > 
> > OOI, why does the code care which CPUs are online rather than just the
> > total number (IOW why a bitmap)?
> 
> When doing strict CPU pinning,the openstack scheduler needs to have the
> list of all pCPUs available in the host. It then tries to place guests
> on pCPUs such that the guest does not span across NUMA nodes. To do this
> it needs to know which particular pCPUs in the host are available. So we
> need the full bitmap rather than just a total count.

Makes perfect sense, thanks.

Ian.