On Wed, 1 Apr 2015 10:01:13 -0300 Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > On Tue, Mar 31, 2015 at 10:09:09PM +0200, Michael Mueller wrote: > > On Tue, 31 Mar 2015 15:35:26 -0300 > > Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > > > > > On Mon, Mar 30, 2015 at 04:28:24PM +0200, Michael Mueller wrote: > > > > This patch implements a new QMP request named 'query-cpu-model'. > > > > It returns the cpu model of cpu 0 and its backing accelerator. > > > > > > > > request: > > > > {"execute" : "query-cpu-model" } > > > > > > > > answer: > > > > {"return" : {"name": "2827-ga2", "accel": "kvm" }} > > > > > > > > Alias names are resolved to their respective machine type and GA names > > > > already during cpu instantiation. Thus, also a cpu model like 'host' > > > > which is implemented as alias will return its normalized cpu model name. > > > > > > > > Furthermore the patch implements the following function: > > > > > > > > - s390_cpu_models_used(), returns true if S390 cpu models are in use > > > > > > > > Signed-off-by: Michael Mueller <mimu(a)linux.vnet.ibm.com&gt; > > > > --- > > > [...] > > > > +static inline char *strdup_s390_cpu_name(S390CPUClass *cc) > > > > +{ > > > > + return g_strdup_printf("%04x-ga%u", cc->proc.type, cc->mach.ga); > > > > +} > > > > > > How exactly is this information going to be used by clients? If getting > > > the correct type and ga values is important for them, maybe you could > > > add them as integer fields, instead of requiring clients to parse the > > > CPU model name? > > > > The consumer don't need to parse the name, it is just important for them to have > > distinctive names that correlate with the names returned by query-cpu-definitions. > > Once the name of an active guest is known, e.g. ("2827-ga2", "kvm") a potential > > migration target can be verified, i.e. its query-cpu-definitions answer for "kvm" > > has to contain "2827-ga2" with the attribute runnable set to true. With that mechanism > > also the largest common denominator can be calculated. That model will be used then. > > Understood. So the point is to really have a name that can be found at > query-cpu-definitions. Makes sense. > > (BTW, if you reused strdup_s390_cpu_name() inside > s390_cpu_compare_class_name() too, you would automatically ensure that > query-cpus, query-cpu-definitions and s390_cpu_class_by_name() will > always agree with each other). I have to verify but it seems to make sense from reading... I will do that if it works. :-) > > > > > I also changed the above mentioned routine to map the cpu model none case: > > > > static inline char *strdup_s390_cpu_name(S390CPUClass *cc) > > { > > if (cpuid(cc->proc)) { > > return g_strdup_printf("%04x-ga%u", cc->proc.type, cc->mach.ga); > > } else { > > return g_strdup("none"); > > } > > } > > What about: > > static const char *s390_cpu_name(S390CPUClass *cc) > { > return cc->model_name; > } > > And then you can just set cc->model_name=_name inside S390_PROC_DEF (and > set it to "none" inside s390_cpu_class_init()). > Wouldn't that store redundant information... but it would at least shift the work into the initialization phase and do the format just once per model.

> I wonder if this class->model_name conversion could be made generic > inside the CPU class. We already have a CPU::class_by_name() method, so > it makes sense to have the opposite function too. > > (But I wouldn't mind making this s390-specific first, and converted > later to generic code if appropriate). ok > > > > > This implicitly will fail a comparison for cpu model ("none", "kvm") as that will > > never be part of the query-cpu-definitions answer. > > I am not sure I follow. If ("none", "kvm") is never in the list, is > "-cpu none -machine accel=kvm" always an invalid use case? Not directly invalid as "-cpu none" will be the same as omitting the -cpu option. KVM will setup the vcpu properties withou any QEMU control to whatever the hosting machine and the kvm kernel code offers. That will allow to run QEMU against a KVM version that is not aware of the s390 cpu model ioctls.

> > (I don't understand completely the meaning of "-cpu none" yet. How does > the CPU look like for the guest in this case? Is it possible to > live-migrate when using -cpu none?) And yes, that does not make sense in a migration context. The answer on query-cpu-model (or query-cpus) will be ("none", "kvm") and that will never match a runnable model. The guest cpu will be derived from the hosting system and the kvm kernel as it is currently without the cpu model interface. I hope I made it better to understand now...