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Re: [Qemu-ppc] [Qemu-devel] [PATCH v5 00/10] sPAPR CPU hotplug
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [Qemu-devel] [PATCH v5 00/10] sPAPR CPU hotplug |
Date: |
Tue, 1 Dec 2015 12:43:21 +1100 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
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_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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- Re: [Qemu-ppc] [PATCH v5 08/10] spapr: CPU hotplug support, (continued)
- [Qemu-ppc] [PATCH v5 03/10] exec: Do vmstate unregistration from cpu_exec_exit(), Bharata B Rao, 2015/11/20
- [Qemu-ppc] [PATCH v5 09/10] spapr: CPU hot unplug support, Bharata B Rao, 2015/11/20
- [Qemu-ppc] [PATCH v5 10/10] target-ppc: Enable CPU hotplug for POWER8 CPU family, Bharata B Rao, 2015/11/20
- [Qemu-ppc] [PATCH v5 01/10] vl: Don't allow CPU toplogies with partially filled cores, Bharata B Rao, 2015/11/20
- Re: [Qemu-ppc] [Qemu-devel] [PATCH v5 00/10] sPAPR CPU hotplug, Peter Krempa, 2015/11/23