Re: [libvirt] [PATCH 0/4] qemu: Use host-model CPU on s390 by default

On Mon, Nov 18, 2019 at 18:34:36 +0100, Boris Fiuczynski wrote: > > > On 11/15/19 4:14 PM, Jiri Denemark wrote: >> On Fri, Nov 15, 2019 at 15:55:04 +0100, Christian Borntraeger wrote: >>> >>> >>> On 15.11.19 15:47, Jiri Denemark wrote: >>>> On Fri, Nov 15, 2019 at 15:12:18 +0100, Boris Fiuczynski wrote: >>>>> Just a heads up. >>>>> After installing libvirt rpms of this branch all my existing kvm s390 >>>>> domains ended up with >>>>> >>>>> <cpu mode='custom' match='exact' check='none'> >>>>> <model fallback='forbid'>qemu</model> >>>>> </cpu> >>>>> >>>>> Newly defined domains without specified cpu do so as well. >>>> >>>> Unless the domains are all TCG, it seems your QEMU is too old. You need >>>> a fairly recent one which contains commit v4.1.0-1683-gde60a92ea7 >>>> (s390x/kvm: Set default cpu model for all machine classes) >>>> >>>> I the domains all use KVM and you have new enough QEMU, there might be a >>>> bug somewhere. Which should not happen :=) >>> >>> So shouldnt libvirt fence this rework (add default model) to qemu 4.2 and newer? >> >> Libvirt does all this only if query-machines returns default-cpu-type, >> which is introduced in 4.2. But since it was introduced earlier, anyone >> using qemu from git between the two commits will see this behavior. >> Somewhat similar thing will happen on ppc64, but even with the current >> master. Everything should be OK once QEMU 4.2.0 final release is used, >> though (since it will contain all required patches). >> >> Jirka >> > > I tested with a newer version of qemu and it worked as you outlined. > After that I also tested with qemu v4.1.0. I was a bit surprised at > first that a default host-model cpu was generated since I though it > would only be done when the qemu has the commit your specified above. > After reading your patch 4 the generation is tied to the cpu-model > support in qemu. Since this became available on s390 with qemu v2.8.0 I > created an additional test patch just to ensure that we do not lose > backwards compatibility. Oh, are you saying QEMU on s390 returns default-cpu-type in query-machines reply even with v4.1.0 and older? I don't see it in our test replies from anything older then v4.2.0. Anyway, libvirt should not set the default CPU with QEMU 4.1.0 and if it does, I have a bug in my patches :-)

qemuDomainDefSetDefaultCPU should not be called at all on QEMU 4.1.0 or older. The check for cpu-model support in this function is an additional check and this support should not be sufficient for the default CPU to be filled in. Jirka -- libvir-list mailing list libvir-list(a)redhat.com https://www.redhat.com/mailman/listinfo/libvir-list