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

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.