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

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.

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