On Fri, Jun 22, 2018 at 02:19:52PM +0200, Jiri Denemark wrote: > On Tue, Jun 12, 2018 at 10:58:46 +0200, Kashyap Chamarthy wrote: [...] > > diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in > > index 6912762f28..4d6c3892ee 100644 > > --- a/docs/formatdomain.html.in > > +++ b/docs/formatdomain.html.in > > @@ -1566,8 +1566,17 @@ > > > > <dl> > > <dt><code>force</code></dt> > > - <dd>The virtual CPU will claim the feature is supported regardless > > - of it being supported by host CPU.</dd> > > The original content was indented. Also I don't think you're supposed to > add two <dd> elements after single <dt>. Hmm, I made a test locally to see it renders as intented. Because, I wnated the second paragraph to be on a separate line. > > > + <dd>The virtual CPU will claim the feature is supported > > + regardless of it being supported by host CPU -- this is only > > + true for QEMU version older than 2.9.0. > > I'd suggest > > Libvirt will ask the hypervisor to enable the feature regardless of > it being supported by host CPU. The hypervisor will likely ignore > this request if the feature is not supported by the host CPU or if > it cannot be emulated. In other words, it is useful for features > which do not exist in real hardware, such as 'virt-ssbd', or which > can be emulated, such as 'x2apic'. Yes, your wording is much clearer. > > I.e. when using the > > + CPU mode 'host-model', libvirt identifies which CPU features > > + to use by looking at host CPUID. For that to take effect, it > > + is mandatory to use <code>force</code> to tell libvirt that a > > + said CPU feature must be used despite it not existing in the > > + host -- this applicable only for a very limited set of CPU > > + features, such as 'x2apic', virt-ssbd' (for AMD CPUs).</dd> > > + <dd>However, when using QEMU 2.9.0 and above, there should > > + never be any need to use <code>force</code>.</dd> > > What was the motivation behind this change? I find it quite confusing > that this is supposed to describe 'force' policy and suddenly you're > talking about host-model CPU mode. Hmm, re-reading, indeed the flow from the previous sentence to the "I.e. when using the CPU mode 'host-model'" seems like a non-sequitur. My intention was to add a note about in which scenarios specifying 'force' makes sense. IIRC, I learnt from Dan Berrangé that if you are using a QEMU version that is older than 2.9.0, then 'force' is required for a guest that needs features that don't exist in the real CPU. If you are using QEMU >= 2.9.0, then 'force' is not required. -- /kashyap -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
