On Tue, 08 Apr 2014 21:47:39 +1000 Alexey Kardashevskiy <a...@ozlabs.ru> wrote:
> On 04/08/2014 08:32 PM, Michael Mueller wrote: > > On Tue, 08 Apr 2014 20:04:42 +1000 > > Alexey Kardashevskiy <a...@ozlabs.ru> wrote: > > > >> On 04/08/2014 07:47 PM, Michael Mueller wrote: > >>> On Tue, 08 Apr 2014 11:23:14 +1000 > >>> Alexey Kardashevskiy <a...@ozlabs.ru> wrote: > >>> > >>>> On 04/08/2014 04:53 AM, Andreas Färber wrote: > >>>>> Am 07.04.2014 05:27, schrieb Alexey Kardashevskiy: > >>>>>> On 04/04/2014 11:28 PM, Alexander Graf wrote: > >>>>>>> On 04/04/2014 07:17 AM, Alexey Kardashevskiy wrote: > >>>>>>>> On 03/24/2014 04:28 PM, Alexey Kardashevskiy wrote: > >>>>>>>>> Currently only migration fails if CPU version is different even a > >>>>>>>>> bit. > >>>>>>>>> For example, migration from POWER7 v2.0 to POWER7 v2.1 fails > >>>>>>>>> because of > >>>>>>>>> that. Since there is no difference between CPU versions which could > >>>>>>>>> affect migration stream, we can safely enable it. > >>>>>>>>> > >>>>>>>>> This adds a helper to find the closest POWERPC family class (i.e. > >>>>>>>>> first > >>>>>>>>> abstract class in hierarchy). > >>>>>>>>> > >>>>>>>>> This replaces VMSTATE_UINTTL_EQUAL statement with a custom handler > >>>>>>>>> which > >>>>>>>>> checks if the source and destination CPUs belong to the same family > >>>>>>>>> and > >>>>>>>>> fails if they are not. > >>>>>>>>> > >>>>>>>>> This adds a PVR reset to the default value as it will be overwritten > >>>>>>>>> by VMSTATE_UINTTL_ARRAY(env.spr, PowerPCCPU, 1024). > >>>>>>>>> > >>>>>>>>> Since the actual migration format is not changed by this patch, > >>>>>>>>> @version_id of vmstate_ppc_cpu does not have to be changed either. > >>>>>>>>> > >>>>>>>>> Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com> > >>>>>>>>> Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > >>>>>>>> > >>>>>>>> Ping? > >>>>>>> > >>>>>>> Can't we just always allow migration to succeed? It's a problem of > >>>>>>> the tool > >>>>>>> stack above if it allows migration to an incompatible host, no? > >>>>>> > >>>>>> This is not how libvirt works. It simply sends the source XML, > >>>>>> reconstructs > >>>>>> a guest on the destination side and then migrates. hoping that the > >>>>>> migration will fail is something (which only QEMU has knowledge of) is > >>>>>> incompatible. The new guest will start with "-cpu host" (as the > >>>>>> source) but > >>>>>> it will create diffrent CPU class and do different things. If we do not > >>>>>> check PVR (and cpu_dt_id and chip_id - the latter is coming soon) and > >>>>>> migrate power8->power7, we can easily get a broken guest. > >>>>> > >>>>> The response is very simple: -cpu host is not supported for migration. > >>>>> Same as for x86 hosts. > >>>> > >>>> Is there any good reason to limit ourselves on POWERPC? > >>>> > >>>>> As you say, the domain config is transferred by libvirt: > >>>>> If you use -cpu POWER7, you can migrate from POWER7 to POWER8 and back; > >>>>> if you use -cpu POWER8, you can only migrate on POWER8. > >>>> > >>>> -cpu other that "host" is not supported by HV KVM, only "compat" which > >>>> upstream QEMU does not have yet. So you are saying that the migration is > >>>> not supported by upstream QEMU for at least SPAPR. Well, ok, it is dead > >>>> anyway so I am fine :) > >>>> > >>> > >>> With s390x we have a similar situation. Thus we came up with a mechanism > >>> to limit > >>> the CPU functionality of a possible target system. Our patch implements > >>> CPU models > >>> based on TYPE and GA like 2817-ga1, etc. (GA represents a CPU facility > >>> set and an IBC > >>> value (Instruction Blocking Control, reduces the instruction set to the > >>> requested > >>> level)) When a guest is started, it receives its CPU model by means of > >>> option -cpu. > >>> "host" equates the configuration of the current system. We implemented > >>> "query-cpu-model" > >>> returning the actual model, here maybe { name: "2817-ga1" }. To find a > >>> suitable > >>> migration target in a remote CEC, libvirt has to "query-cpu-definitions" > >>> returning a > >>> list of models supported by the target system "{{name: "2827-ga2"}, > >>> {name: "2827-ga1"}, > >>> {name: "2817-ga2"},...]. A match means the system is suitable and can be > >>> used > >>> as migration target. > >> > >> Sorry, I do not follow you. You hacked libvirt to run the destination QEMU > >> with a specific CPU model? Or it is in QEMU? Where? What I see now is this: > >> > >> static const VMStateDescription vmstate_s390_cpu = { > >> .name = "cpu", > >> .unmigratable = 1, > >> }; > >> > >> Does not look like it supports migration :) Thanks! > >> > > > > The code you're missing is not upstream yet. The s390x guest can be > > migrated in the meantime. > > Yes, libvirt currently gets an extension to be able to identify and startup > > suitable migration > > targets for s390x on behalf of the mentioned qemu cpu model. BTW can you > > point me to the above > > mentioned SPAPR stuff... > > > Mmm. What stuff? :) At the moment POWERPC guests migrate if PVR (processor > version register) value is exactly the same. I am trying to relax this > limitation to any version within same CPU family, like power7 v1.0 and v2.1. With stuff I referred to to term sPAPR not realizing it relates to the Power Architecture Platform Requirements, got it now. :-) I see, ppc currently has this limitation to enforce compatibility VMSTATE_UINTTL_EQUAL(env.spr[SPR_PVR], PowerPCCPU), Thanks Michael > > >