From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51851) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WXScz-0005BN-ML for qemu-devel@nongnu.org; Tue, 08 Apr 2014 05:47:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WXSco-00047T-23 for qemu-devel@nongnu.org; Tue, 08 Apr 2014 05:47:37 -0400 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:43317) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WXScn-00046Y-PB for qemu-devel@nongnu.org; Tue, 08 Apr 2014 05:47:25 -0400 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 8 Apr 2014 10:47:23 +0100 Date: Tue, 8 Apr 2014 11:47:16 +0200 From: Michael Mueller Message-ID: <20140408114716.2893645e@bee> In-Reply-To: <53434F82.80703@ozlabs.ru> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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: Alexey Kardashevskiy Cc: qemu-devel@nongnu.org, Alexander Graf , qemu-ppc@nongnu.org, Andreas =?UTF-8?B?RsOkcmJlcg==?= , Bharata B Rao 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 even a b= it. > >>>>> For example, migration from POWER7 v2.0 to POWER7 v2.1 fails becaus= e 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. f= irst > >>>>> 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 > >>>>> Signed-off-by: Alexey Kardashevskiy > >>>> > >>>> Ping? > >>> > >>> Can't we just always allow migration to succeed? It's a problem of th= e tool > >>> stack above if it allows migration to an incompatible host, no? > >> > >> This is not how libvirt works. It simply sends the source XML, reconst= ructs > >> 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. > >=20 > > The response is very simple: -cpu host is not supported for migration. > > Same as for x86 hosts. >=20 > Is there any good reason to limit ourselves on POWERPC? >=20 > > 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. >=20 > -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 :) >=20 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 req= uested level)) When a guest is started, it receives its CPU model by means of opti= on -cpu. "host" equates the configuration of the current system. We implemented "que= ry-cpu-model" returning the actual model, here maybe { name: "2817-ga1" }. To find a suit= able migration target in a remote CEC, libvirt has to "query-cpu-definitions" re= turning 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 us= ed as migration target. Thanks Michael