On 02/15/2017 11:44 AM, Jiri Denemark wrote: > Signed-off-by: Jiri Denemark <jdenemar@xxxxxxxxxx> > --- > > Notes: > Version 2: > - no change > > docs/formatdomain.html.in | 28 ++++++++++++++++++---------- > 1 file changed, 18 insertions(+), 10 deletions(-) > I would think this should be merged with the previous patch, but it's not necessary... > 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... > + 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/ > + 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." 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? ACK with a couple of tweaks John > + (for example, domains with type <code>kvm</code>). The actual host CPU > + is irrelevant for domains with emulated virtual CPUs (such as domains > + with type <code>qemu</code>). However, for backward compatibility > + <code>host-model</code> may be implemented even for domains running on > + emulated CPUs in which case the best CPU the hypervisor is able to > + emulate may be used rather then trying to mimic the host CPU model. > </dd> > > <dt><code>model</code></dt> > -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
