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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jun 14, 2016 at 05:34:22PM +0100, Ian Jackson wrote:
> Wei Liu writes ("Re: [Xen-devel] "xl vcpu-set" not persistent across 
> reboot?"):
> > On Mon, Jun 06, 2016 at 06:34:44PM +0100, Andrew Cooper wrote:
> > > Why does qemu even care?  It has nothing to do with vcpu handling. 
> > > There should not be any qemu vcpu records in the first place.
> > 
> > IIRC upstream rejected the idea of having no cpu attached to a platform.
> 
> That doesn't explain why the number of vcpus that qemu believes in has
> to have anything to do with the number of vcpus that the guest has.
> 
> The qemu vcpu state is a dummy, regardless of how many of it there
> are, surely ?
> 

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.

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.

The guest is irrelevant here. We don't care about what guest thinks, but
we need to keep toolstack side view consistent so that migration and
save / restore won't fail.

Wei.

> Ian.

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