Re: [libvirt] [PATCHv2 11/11] qemu_driver: BaselineHypervisorCPU supports S390 using QEMU/QMP

On 07/21/2018 12:05 AM, Chris Venteicher wrote: > Quoting David Hildenbrand (2018-07-18 02:26:24) >> On 18.07.2018 00:39, Collin Walling wrote: >>> On 07/17/2018 05:01 PM, David Hildenbrand wrote: >>>> On 13.07.2018 18:00, Jiri Denemark wrote: >>>>> On Mon, Jul 09, 2018 at 22:56:55 -0500, Chris Venteicher wrote: >>>>>> Transient S390 configurations require using QEMU to compute CPU Model >>>>>> Baseline and to do CPU Feature Expansion. >>>>>> >>>>>> Start and use a single QEMU instance to do both the baseline and >>>>>> expansion transactions required by BaselineHypervisorCPU. >>>>>> >>>>>> CPU Feature Expansion uses true / false to indicate if property is/isn't >>>>>> included in model. Baseline only returns property list where all >>>>>> enumerated properties are included. >>>>> >>>>> So are you saying on s390 there's no chance there would be a CPU model >>>>> with some feature which is included in the CPU model disabled for some >>>>> reason? Sounds too good to be true :-) (This is the question I referred >>>>> to in one of my replies to the other patches.) >>>> >>>> Giving some background information: When we expand/baseline CPU models, >>>> we always expand them to the "-base" variants of our CPU models, which >>>> contain some set of features we expect to be around in all sane >>>> configurations ("minimal feature set"). >>>> >>>> It is very unlikely that we ever have something like >>>> "z14-base,featx=off", but it could happen >>>> - When using an emulator (TCG) >>>> - When running nested and the guest hypervisor is started with such a >>>> strange CPU model >>>> - When something in the HW is very wrong or eventually removed in the >>>> future (unlikely but possible) >>>> >>>> On some very weird inputs to a baseline request, such a strange model >>>> can also be the result. But it is very unusual. >>>> >>>> I assume something like "baseline z14-base,featx=off with z14-base" will >>>> result in "z14-base,featx=off", too. >>>> >>>> >>> >>> That's correct. A CPU model with a feature disabled that is baseline with a CPU >>> model with that same feature enabled will omit that feature in the QMP response. >>> >>> e.g. if z14-base has features x, y, z then >>> >>> "baseline z14-base,featx=off with z14-base" will result in "z14-base,featy=on,featz=on" > > I am runing tests on both S390 and X86 (hacked QEMU to enable baseline). > > I don't see a "false" property in the baseline response in any of the logs. Right... baseline should not be returning any properties paired with false. It constructs a third CPU model with properties that can run on both CPUs.