Re: [libvirt] Cpu Modeling

On 09/23/2016 08:05 AM, Jiri Denemark wrote: > On Thu, Sep 22, 2016 at 14:47:36 -0400, Jason J. Herne wrote: ... >> 1. We will invoke qemu to gather the host cpu data used for virsh >> capabilities. Today this data seems to be collected directly from the >> host hardware for most (all?) architectures. > > Not really, virsh capabilities will still contain data gathered directly > from the host hardware. But, we have virsh domcapabilities for > displaying data tight to a specific QEMU binary. Since yesterday > afternoon we have support for displaying CPU related data in the domain > capabilities XML; see > http://libvirt.org/formatdomaincaps.html#elementsCPU > The host-model part of the XML will show the result of > query-cpu-model-expansion on "host" model, or the result of querying the > hardware directly if we can't ask QEMU for that (which is the current > state). So the expectation here is that virsh capabilities" reports actual host cpu data. So for S390, we can leave our implementation of this "as-is" and not report any features here, I'm guessing. And the <cpu> section from virsh domcapabilities will contain the Qemu specific supported cpu modeling info. As you stated <mode name='host-model'> will contain the name (and possibly feature details?) of the model returned by qmp query-model-expansion on 'host'. Furthermore, the <mode name='custom'> section will list all supported model names, as indicated by qmp query-cpu-definitions. Do I have it right? >> 2. virsh cpu-models {arch} will also use a Qemu invocation to gather >> cpu model data. > > No, virsh cpu-models will just list CPU models supported by libvirt So, in other words we just spit out whatever models Libvirt managed to grab, and cache, from a call to qmp query-cpu-definitions? Or am I missing something? > (or an empty list if libvirt supports all models supported by QEMU). Can you clarify? It seems odd that an empty list would be returned here. I thought the point was to list all supported cpu models. For x86 today I imagine it is the list found in cpu_map.xml. For s390, this will be the list we get back from qmp query-cpu-definitions, which as you mention below, is found in the domain capabilities XML. > The CPU model data from QEMU can be found in domain capabilities XML. > >> 3. Most architectures seem to use a "map" (xml file containing cpu >> model data that ships with Libvirt) to satisfy #1 and #2 above. Our >> new method does not use this map as it gets all of the data directly >> from Qemu. > > Even if we switch some CPU operations to work through QEMU, we may still > need to use the cpu_map.xml file for some other operations, or other > hypervisor driver. It all depends on what we need to do for a given > architecture. For example, ARM does not use cpu_map.xml at all even now. > > Slightly related, I don't think we have a way to list CPU features > supported by QEMU over QMP, do we? "-cpu ?" will show them all, but I > couldn't find a QMP command that would give me the same list. > query-model-expansion will return all features of a given model name. Model names can be enumerated via query-cpu-definitions. >> 4. virsh cpu-baseline and cpu-compare will now invoke qemu directly as >> well. > > Perhaps, but before we can do that, we'll probably need to come up with > new APIs. It don't think it's critical, though. Do you mind elaborating on this a bit? Which APIs do we want to look at here? Are you talking about new commands/calls to replace cpu-baseline and cpu-compare? Thanks again for your time.