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Re: [libvirt] [PATCH v2 08/33] docs: Update description of the host-model CPU mode



On Tue, Feb 21, 2017 at 09:25:28 -0500, John Ferlan wrote:
> > diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> > index 294d3c467..9e7f7804e 100644
> > --- a/docs/formatdomain.html.in
> > +++ b/docs/formatdomain.html.in
> > @@ -1272,16 +1272,15 @@
> >            model even if the destination host contains more capable CPUs for
> >            the running instance of the guest; but shutting down and restarting
> >            the guest may present different hardware to the guest according to
> > -          the capabilities of the new host. <strong>Beware</strong>, due to the
> > -          way libvirt detects host CPU and due to the fact libvirt does not
> > -          talk to QEMU/KVM when creating the CPU model, CPU configuration
> > -          created using <code>host-model</code> may not work as expected. The
> > -          guest CPU may differ from the configuration and it may also confuse
> > -          guest OS by using a combination of CPU features and other parameters
> > -          (such as CPUID level) that don't work. Until these issues are fixed,
> > -          it's a good idea to avoid using <code>host-model</code> and use
> > -          <code>custom</code> mode with just the CPU model from host
> > -          capabilities XML.
> > +          the capabilities of the new host. Libvirt older than 3.1.0 or QEMU
> > +          older than 2.9.0 do not support detection of the host CPU model via
> 
> How about:
> 
> Prior to libvirt 3.1.0 and QEMU 2.9.0 detection of the host CPU model
> via QEMU is not supported. Thus the CPU...

Yeah, this is better.

> 
> > +          QEMU and thus the CPU configuration created using
> > +          <code>host-model</code> may not work as expected.
> > +          <span class="since">3.1.0 and QEMU 2.9.0</span> this mode works the
> 
> s/3.1.0/Since 3.1.0/

Oops.

> 
> > +          way it was designed and it is indicated by the <code>fallback</code>
> > +          attribute set to <code>forbid</code> in the host-model CPU
> > +          definition advertised in <a href="formatdomaincaps.html#elementsCPU"
> > +          >domain capabilities XML</a>.
> 
> You may want to keep some simple text to describe what to do for
> releases prior to 3.1.0/2.9.0... e.g. "Without the proper support, it's
> recommended to use <code>custom</code> mode with just the CPU model from
> the host capabilities XML."

Sure. Good idea.

> 
> Your call on this part - it's just me thinking of those who read this
> documentation that do not have 3.1.0 and 2.9.0...
> 
> 
> >            <span class="since">Since 1.2.11</span> PowerISA allows
> >            processors to run VMs in binary compatibility mode supporting an
> >            older version of ISA.  Libvirt on PowerPC architecture uses the
> > @@ -1307,6 +1306,15 @@
> >            a migration is attempted then the guest may hang or crash upon
> >            resuming execution on the destination host.</dd>
> >          </dl>
> > +
> > +        Both <code>host-model</code> and <code>host-passthrough</code> modes
> > +        make sense when a domain can run directly on the host CPUs without
> 
> without what?

Without "without" :-) s/without//

Jirka


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