On Mon, Nov 23, 2015 at 02:04:46PM +0100, Christian Borntraeger wrote: > On 11/23/2015 12:54 PM, Peter Krempa wrote: > > On Fri, Nov 20, 2015 at 18:24:29 +0530, Bharata B Rao wrote: > >> This patchset adds CPU hotplug support for sPAPR PowerPC guests using > >> device_add and device_del commands > >> > >> (qemu) device_add POWER8-powerpc64-cpu,id=cpu0 > > > > Is there a reason why this uses 'device_add' rather than the 'cpu_add' > > command? Libvirt uses two separate approaches already. Due to legacy > > reasons we support the HMP 'cpu_set' command, and lately we added > > support for QMP 'cpu-add'. Using device_add here will introduce a > > different approach and will require yet another compatibility layer in > > libvirt to support this. > > s390 and powerpc both started with cpu_add patches. Andreas Faerber > suggested then to only implement device_add. This was apparently discussed > at the last KVM forum.
This may not be the only reason, but one problem with cpu_add is that
the interface is strictly per-vcpu, i.e. per-thread. That doesn't
work for Power guests, because the PAPR interface used to communicate
to the guest can only work at a core granularity.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
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