From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55604) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WXStl-0002dQ-8d for qemu-devel@nongnu.org; Tue, 08 Apr 2014 06:05:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WXStd-0004Cc-VU for qemu-devel@nongnu.org; Tue, 08 Apr 2014 06:04:56 -0400 Received: from mail-pa0-f48.google.com ([209.85.220.48]:53150) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WXStd-0004CI-Mi for qemu-devel@nongnu.org; Tue, 08 Apr 2014 06:04:49 -0400 Received: by mail-pa0-f48.google.com with SMTP id hz1so818244pad.7 for ; Tue, 08 Apr 2014 03:04:48 -0700 (PDT) Message-ID: <5343C9BA.2030806@ozlabs.ru> Date: Tue, 08 Apr 2014 20:04:42 +1000 From: Alexey Kardashevskiy 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> In-Reply-To: <20140408114716.2893645e@bee> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: qemu-devel@nongnu.org, Alexander Graf , qemu-ppc@nongnu.org, =?UTF-8?B?QW5kcmVhcyBGw6RyYmVy?= , Bharata B Rao 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 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 >>>>>>> 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, 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! -- Alexey