Re: [Xen-devel] "xl vcpu-set" not persistent across reboot?

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Tue, Jun 14, 2016 at 05:57:00PM +0100, Ian Jackson wrote:
> Wei Liu writes ("Re: [Xen-devel] "xl vcpu-set" not persistent across 
> reboot?"):
> > What Andrew means is that QEMU shouldn't have kept the CPU state
> > structures in the first place. My response explains why that is not
> > possible from a QEMU upstream point of view.
> 
> I don't think it addresses my point.
> 
> > Hence the unfortunate fact is that we need to live with it for now. To
> > start QEMU we need to create a bunch of dummy CPUs to keep QEMU happy.
> > All those dummy states need to be kept.
> 
> Why do we need one dummy state per actual vcpu rather than just one
> dummy state no matter how many vcpus ?
> 
> Or is qemu involved in hvm cpu hotplug ?

It is, QEMU does the notification to the guest of a newly available CPU
via an ACPI GPE or something like that. I think QEMU manage the bitfield
of online CPUs then notify the guest about changes.

-- 
Anthony PERARD

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