From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41528) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WXXVF-0004Op-7W for qemu-devel@nongnu.org; Tue, 08 Apr 2014 11:00:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WXXV8-0000Cx-T6 for qemu-devel@nongnu.org; Tue, 08 Apr 2014 10:59:57 -0400 Message-ID: <53440EE5.2000004@suse.de> Date: Tue, 08 Apr 2014 16:59:49 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1395638892-24481-1-git-send-email-aik@ozlabs.ru> <533E4050.3030705@ozlabs.ru> <533EA582.4090206@suse.de> <53421B2E.2060301@ozlabs.ru> <5342F446.6040303@suse.de> <53434F82.80703@ozlabs.ru> <20140408114716.2893645e@bee> <5343C9BA.2030806@ozlabs.ru> <20140408123252.67fc7ce3@bee> <5343E1DB.6010302@ozlabs.ru> <20140408141923.22e780a7@bee> In-Reply-To: <20140408141923.22e780a7@bee> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC PATCH] target-ppc: enable migration within the same CPU family List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Michael Mueller Cc: Alexey Kardashevskiy , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= , Bharata B Rao On 04/08/2014 02:19 PM, Michael Mueller wrote: > On Tue, 08 Apr 2014 21:47:39 +1000 > Alexey Kardashevskiy wrote: > >> On 04/08/2014 08:32 PM, Michael Mueller wrote: >>> On Tue, 08 Apr 2014 20:04:42 +1000 >>> Alexey Kardashevskiy wrote: >>> >>>> On 04/08/2014 07:47 PM, Michael Mueller wrote: >>>>> On Tue, 08 Apr 2014 11:23:14 +1000 >>>>> Alexey Kardashevskiy wrote: >>>>> >>>>>> On 04/08/2014 04:53 AM, Andreas F=C3=A4rber 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 ev= en 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 ha= ndler 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 over= written >>>>>>>>>>> by VMSTATE_UINTTL_ARRAY(env.spr, PowerPCCPU, 1024). >>>>>>>>>>> >>>>>>>>>>> Since the actual migration format is not changed by this patc= h, >>>>>>>>>>> @version_id of vmstate_ppc_cpu does not have to be changed ei= ther. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: Bharata B Rao >>>>>>>>>>> Signed-off-by: Alexey Kardashevskiy >>>>>>>>>> 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, r= econstructs >>>>>>>> a guest on the destination side and then migrates. hoping that t= he >>>>>>>> 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 migra= tion. >>>>>>> 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" w= hich >>>>>> upstream QEMU does not have yet. So you are saying that the migrat= ion 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 mech= anism to limit >>>>> the CPU functionality of a possible target system. Our patch implem= ents CPU models >>>>> based on TYPE and GA like 2817-ga1, etc. (GA represents a CPU facil= ity 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 implemen= ted "query-cpu-model" >>>>> returning the actual model, here maybe { name: "2817-ga1" }. To fin= d a suitable >>>>> migration target in a remote CEC, libvirt has to "query-cpu-definit= ions" 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 c= an be used >>>>> as migration target. >>>> Sorry, I do not follow you. You hacked libvirt to run the destinatio= n QEMU >>>> with a specific CPU model? Or it is in QEMU? Where? What I see now i= s this: >>>> >>>> static const VMStateDescription vmstate_s390_cpu =3D { >>>> .name =3D "cpu", >>>> .unmigratable =3D 1, >>>> }; >>>> >>>> Does not look like it supports migration :) Thanks! >>>> >>> The code you're missing is not upstream yet. The s390x guest can be m= igrated in the meantime. >>> Yes, libvirt currently gets an extension to be able to identify and s= tartup 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 (proce= ssor >> 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), Yes, but the s390 approach is a lot cleaner and I'd rather like to move=20 into that direction. Alex