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Re: [Qemu-devel] [PATCH v4 14/18] target-i386: Add "migratable" property

From: Eduardo Habkost
Subject: Re: [Qemu-devel] [PATCH v4 14/18] target-i386: Add "migratable" property to "host" CPU model
Date: Fri, 16 May 2014 13:13:05 -0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Fri, May 16, 2014 at 12:12:18AM +0200, Andreas Färber wrote:
> Am 15.05.2014 22:26, schrieb Eduardo Habkost:
> > On Thu, May 15, 2014 at 09:44:49PM +0200, Andreas Färber wrote:
> >> Am 30.04.2014 18:48, schrieb Eduardo Habkost:
> >>> This flag will allow the user to choose between two modes:
> >>>  * All flags that can be enabled on the host, even if unmigratable
> >>>    (migratable=no);
> >>>  * All flags that can be enabled on the host, known to QEMU,
> >>>    and migratable (migratable=yes).
> >>>
> >>> The default is still migratable=false, to keep current behavior, but
> >>> this will be changed to migratable=true by another patch.
> >>>
> >>> My plan was to support the "migratable" flag on all CPU classes, but
> >>> have the default to "false" on all CPU models except "host". However,
> >>> DeviceClass has no mechanism to allow a child class to have a different
> >>> property default from the parent class yet, so by now only the "host"
> >>> CPU model will support the "migratable" flag.
> >>
> >> Just set the new default in the derived type's instance_init?
> > 
> > That would work. I am still assuming that one day we will allow
> > management to query for class property defaults without instantiating
> > objects. But even if we do it, "host" is already an exception (because
> > the defaults depend on KVM initialization), so in this case it will be
> > OK.
> > 
> > So, this patch can be dropped because it will be replaced. I will also
> > implement the other changes you requested for this patch.
> Before you make yourself too much work, have a peek at qom-cpu. :)
> I should have all except 15 and 18, with some cleanups TBD.

Thsnk! But I see two problems on current qom-cpu:

 * The "migratable" flag is now not affecting the results of "-cpu host"
   (host_x86_cpu_initfn()), which was the whole point of adding the
 * Without setting migratable=yes by default, we are going to break
   existing setups after applying 'support "invariant tsc" flag' and
   "block migration and savevm if invariant tsc is exposed" (See
   http://marc.info/?l=qemu-devel&m=139838802220184&w=2 ).


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